diff --git a/.gitignore b/.gitignore
index ec5ebb2345..aa79760566 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,6 +12,10 @@ docker/*.sql.xz
 .idea
 .vscode
 
+# macOS
+.DS_Store
+**/.DS_Store
+
 # local build files
 target
 env_setup.sh
diff --git a/Cargo.lock b/Cargo.lock
index 78f5e41450..180c3c87c0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3528,6 +3528,7 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_with",
+ "sha2",
  "strum 0.28.0",
  "tracing",
  "url",
diff --git a/crates/apub/activities/Cargo.toml b/crates/apub/activities/Cargo.toml
index b43b0e038a..b19055d68b 100644
--- a/crates/apub/activities/Cargo.toml
+++ b/crates/apub/activities/Cargo.toml
@@ -50,6 +50,7 @@ serde_with.workspace = true
 enum_delegate = "0.2.0"
 either = { workspace = true }
 lemmy_diesel_utils = { workspace = true }
+sha2 = "0.10.9"
 
 [dev-dependencies]
 
diff --git a/crates/apub/activities/src/block/block_user.rs b/crates/apub/activities/src/block/block_user.rs
index cc16b0a438..2fa50a76a9 100644
--- a/crates/apub/activities/src/block/block_user.rs
+++ b/crates/apub/activities/src/block/block_user.rs
@@ -5,7 +5,7 @@ use crate::{
   block::{SiteOrCommunity, generate_cc},
   check_community_deleted_or_removed,
   community::send_activity_in_community,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::block::block_user::BlockUser,
   send_lemmy_activity,
 };
@@ -57,7 +57,7 @@ impl BlockUser {
       kind: BlockType::Block,
       remove_data,
       summary: Some(reason),
-      id: generate_activity_id(BlockType::Block, context)?,
+      id: generate_activity_id_with_object_id(BlockType::Block, context)?,
       end_time: expires,
       audience: target.as_ref().right().map(|c| c.ap_id.clone().into()),
     })
diff --git a/crates/apub/activities/src/block/undo_block_user.rs b/crates/apub/activities/src/block/undo_block_user.rs
index 4c7b319073..8060e75b04 100644
--- a/crates/apub/activities/src/block/undo_block_user.rs
+++ b/crates/apub/activities/src/block/undo_block_user.rs
@@ -4,7 +4,7 @@ use crate::{
   activity_lists::AnnouncableActivities,
   block::{SiteOrCommunity, generate_cc},
   community::send_activity_in_community,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::block::{block_user::BlockUser, undo_block_user::UndoBlockUser},
   send_lemmy_activity,
 };
@@ -47,7 +47,7 @@ impl UndoBlockUser {
     let block = BlockUser::new(target, user, mod_, None, reason, None, context).await?;
     let to = to(target)?;
 
-    let id = generate_activity_id(UndoType::Undo, context)?;
+    let id = generate_activity_id_with_object_id(UndoType::Undo, context)?;
     let undo = UndoBlockUser {
       actor: mod_.id().clone().into(),
       to,
diff --git a/crates/apub/activities/src/community/announce.rs b/crates/apub/activities/src/community/announce.rs
index b61c8311d1..ca5ce8fbb1 100644
--- a/crates/apub/activities/src/community/announce.rs
+++ b/crates/apub/activities/src/community/announce.rs
@@ -1,6 +1,6 @@
 use crate::{
   activity_lists::AnnouncableActivities,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   generate_announce_activity_id,
   protocol::{
     IdOrNestedObject,
@@ -83,6 +83,7 @@ impl AnnounceActivity {
   pub fn new(
     object: RawAnnouncableActivities,
     community: &ApubCommunity,
+    object_id: Option<&Url>,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<AnnounceActivity> {
     let inner_kind = object
@@ -90,8 +91,11 @@ impl AnnounceActivity {
       .get("type")
       .and_then(serde_json::Value::as_str)
       .unwrap_or("other");
-    let id =
-      generate_announce_activity_id(inner_kind, &context.settings().get_protocol_and_hostname())?;
+    let id = generate_announce_activity_id(
+      inner_kind,
+      &context.settings().get_protocol_and_hostname(),
+      object_id,
+    )?;
     Ok(AnnounceActivity {
       actor: community.id().clone().into(),
       to: generate_to(community)?,
@@ -112,7 +116,7 @@ impl AnnounceActivity {
     community: &ApubCommunity,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<()> {
-    let announce = AnnounceActivity::new(object.clone(), community, context)?;
+    let announce = AnnounceActivity::new(object.clone(), community, None, context)?;
     let inboxes = ActivitySendTargets::to_local_community_followers(community.id);
     send_lemmy_activity(context, announce, community, inboxes.clone(), false).await?;
 
@@ -123,14 +127,14 @@ impl AnnounceActivity {
       // Hack: need to convert Page into a format which can be sent as activity, which requires
       //       adding actor field.
       let announcable_page = RawAnnouncableActivities {
-        id: generate_activity_id(AnnounceType::Announce, context)?,
+        id: generate_activity_id_with_object_id(AnnounceType::Announce, context)?,
         actor: c.actor.clone().into_inner(),
         other: serde_json::to_value(c.object)?
           .as_object()
           .ok_or(UntranslatedError::Unreachable)?
           .clone(),
       };
-      let announce_compat = AnnounceActivity::new(announcable_page, community, context)?;
+      let announce_compat = AnnounceActivity::new(announcable_page, community, None, context)?;
       send_lemmy_activity(context, announce_compat, community, inboxes, false).await?;
     }
     Ok(())
diff --git a/crates/apub/activities/src/community/collection_add.rs b/crates/apub/activities/src/community/collection_add.rs
index e9618d8c5d..81dd3d19a3 100644
--- a/crates/apub/activities/src/community/collection_add.rs
+++ b/crates/apub/activities/src/community/collection_add.rs
@@ -2,7 +2,7 @@ use crate::{
   activity_lists::AnnouncableActivities,
   check_community_deleted_or_removed,
   community::send_activity_in_community,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::community::{collection_add::CollectionAdd, collection_remove::CollectionRemove},
 };
 use activitypub_federation::{
@@ -46,7 +46,7 @@ impl CollectionAdd {
     actor: &ApubPerson,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<()> {
-    let id = generate_activity_id(AddType::Add, context)?;
+    let id = generate_activity_id_with_object_id(AddType::Add, context)?;
     let add = CollectionAdd {
       actor: actor.id().clone().into(),
       to: generate_to(community)?,
@@ -69,7 +69,7 @@ impl CollectionAdd {
     actor: &ApubPerson,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<()> {
-    let id = generate_activity_id(AddType::Add, context)?;
+    let id = generate_activity_id_with_object_id(AddType::Add, context)?;
     let add = CollectionAdd {
       actor: actor.id().clone().into(),
       to: generate_to(community)?,
diff --git a/crates/apub/activities/src/community/collection_remove.rs b/crates/apub/activities/src/community/collection_remove.rs
index 1c3069f710..f3308f2c21 100644
--- a/crates/apub/activities/src/community/collection_remove.rs
+++ b/crates/apub/activities/src/community/collection_remove.rs
@@ -2,7 +2,7 @@ use crate::{
   activity_lists::AnnouncableActivities,
   check_community_deleted_or_removed,
   community::send_activity_in_community,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::community::collection_remove::CollectionRemove,
 };
 use activitypub_federation::{
@@ -44,7 +44,7 @@ impl CollectionRemove {
     actor: &ApubPerson,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<()> {
-    let id = generate_activity_id(RemoveType::Remove, context)?;
+    let id = generate_activity_id_with_object_id(RemoveType::Remove, context)?;
     let remove = CollectionRemove {
       actor: actor.id().clone().into(),
       to: generate_to(community)?,
@@ -67,7 +67,7 @@ impl CollectionRemove {
     actor: &ApubPerson,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<()> {
-    let id = generate_activity_id(RemoveType::Remove, context)?;
+    let id = generate_activity_id_with_object_id(RemoveType::Remove, context)?;
     let remove = CollectionRemove {
       actor: actor.id().clone().into(),
       to: generate_to(community)?,
diff --git a/crates/apub/activities/src/community/lock.rs b/crates/apub/activities/src/community/lock.rs
index 85b3fa21e1..00aa7f4a31 100644
--- a/crates/apub/activities/src/community/lock.rs
+++ b/crates/apub/activities/src/community/lock.rs
@@ -3,7 +3,7 @@ use crate::{
   activity_lists::AnnouncableActivities,
   check_community_deleted_or_removed,
   community::send_activity_in_community,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   post_or_comment_community,
   protocol::community::lock::{LockPageOrNote, LockType, UndoLockPageOrNote},
 };
@@ -155,7 +155,7 @@ pub(crate) async fn send_lock(
   context: Data<LemmyContext>,
 ) -> LemmyResult<()> {
   let community: ApubCommunity = post_or_comment_community(&object, &context).await?.into();
-  let id = generate_activity_id(LockType::Lock, &context)?;
+  let id = generate_activity_id_with_object_id(LockType::Lock, &context)?;
   let community_id = community.ap_id.inner().clone();
   let ap_id = match object {
     PostOrComment::Left(p) => p.ap_id.clone(),
@@ -175,7 +175,7 @@ pub(crate) async fn send_lock(
   let activity = if locked {
     AnnouncableActivities::Lock(lock)
   } else {
-    let id = generate_activity_id(UndoType::Undo, &context)?;
+    let id = generate_activity_id_with_object_id(UndoType::Undo, &context)?;
     let undo = UndoLockPageOrNote {
       actor: lock.actor.clone(),
       to: generate_to(&community)?,
diff --git a/crates/apub/activities/src/community/report.rs b/crates/apub/activities/src/community/report.rs
index b6592561bb..d8e9ffa0d9 100644
--- a/crates/apub/activities/src/community/report.rs
+++ b/crates/apub/activities/src/community/report.rs
@@ -2,7 +2,7 @@ use super::{local_community, report_inboxes};
 use crate::{
   activity_lists::AnnouncableActivities,
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::community::{
     announce::AnnounceActivity,
     report::{Report, ReportObject},
@@ -57,7 +57,7 @@ impl Report {
     context: &Data<LemmyContext>,
   ) -> LemmyResult<Self> {
     let kind = FlagType::Flag;
-    let id = generate_activity_id(kind.clone(), context)?;
+    let id = generate_activity_id_with_object_id(kind.clone(), context)?;
     Ok(Report {
       actor: actor.id().clone().into(),
       to: [receiver.id().clone().into()],
@@ -172,7 +172,7 @@ impl Activity for Report {
       // forward to remote mods
       let object_id = self.object.object_id(context).await?;
       let announce = AnnouncableActivities::Report(self);
-      let announce = AnnounceActivity::new(announce.try_into()?, community, context)?;
+      let announce = AnnounceActivity::new(announce.try_into()?, community, None, context)?;
       let inboxes = report_inboxes(object_id, &receiver, &actor, context).await?;
       send_lemmy_activity(context, announce, community, inboxes.clone(), false).await?;
     }
diff --git a/crates/apub/activities/src/community/resolve_report.rs b/crates/apub/activities/src/community/resolve_report.rs
index 119c6fb41d..dd6c219131 100644
--- a/crates/apub/activities/src/community/resolve_report.rs
+++ b/crates/apub/activities/src/community/resolve_report.rs
@@ -1,7 +1,7 @@
 use super::{local_community, report_inboxes, verify_mod_or_admin_action};
 use crate::{
   activity_lists::AnnouncableActivities,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::community::{
     announce::AnnounceActivity,
     report::Report,
@@ -47,7 +47,7 @@ impl ResolveReport {
     context: Data<LemmyContext>,
   ) -> LemmyResult<()> {
     let kind = ResolveType::Resolve;
-    let id = generate_activity_id(kind.clone(), &context)?;
+    let id = generate_activity_id_with_object_id(kind.clone(), &context)?;
     let object = Report::new(&object_id, report_creator, receiver, None, &context)?;
     let resolve = ResolveReport {
       actor: actor.id().clone().into(),
@@ -106,7 +106,7 @@ impl Activity for ResolveReport {
       // forward to remote mods
       let object_id = self.object.object.object_id(context).await?;
       let announce = AnnouncableActivities::ResolveReport(self);
-      let announce = AnnounceActivity::new(announce.try_into()?, community, context)?;
+      let announce = AnnounceActivity::new(announce.try_into()?, community, None, context)?;
       let inboxes = report_inboxes(object_id, &receiver, &reporter, context).await?;
       send_lemmy_activity(context, announce, community, inboxes.clone(), false).await?;
     }
diff --git a/crates/apub/activities/src/community/update.rs b/crates/apub/activities/src/community/update.rs
index 434f3526dd..f59f62bf22 100644
--- a/crates/apub/activities/src/community/update.rs
+++ b/crates/apub/activities/src/community/update.rs
@@ -1,7 +1,7 @@
 use crate::{
   check_community_deleted_or_removed,
   community::{AnnouncableActivities, send_activity_in_community},
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::community::update::Update,
   send_lemmy_activity,
 };
@@ -36,7 +36,7 @@ pub(crate) async fn send_update_community(
 ) -> LemmyResult<()> {
   let community: ApubCommunity = community.into();
   let actor: ApubPerson = actor.into();
-  let id = generate_activity_id(UpdateType::Update, &context)?;
+  let id = generate_activity_id_with_object_id(UpdateType::Update, &context)?;
   let update = Update {
     actor: actor.id().clone().into(),
     to: generate_to(&community)?,
@@ -66,7 +66,7 @@ pub(crate) async fn send_update_multi_community(
 ) -> LemmyResult<()> {
   let multi: ApubMultiCommunity = multi.into();
   let actor: ApubPerson = actor.into();
-  let id = generate_activity_id(UpdateType::Update, &context)?;
+  let id = generate_activity_id_with_object_id(UpdateType::Update, &context)?;
   let update = Update {
     actor: actor.id().clone().into(),
     to: vec![multi.ap_id.clone().into(), public()],
diff --git a/crates/apub/activities/src/create_or_update/comment.rs b/crates/apub/activities/src/create_or_update/comment.rs
index f307100ee1..3a131fe5ed 100644
--- a/crates/apub/activities/src/create_or_update/comment.rs
+++ b/crates/apub/activities/src/create_or_update/comment.rs
@@ -55,7 +55,10 @@ impl CreateOrUpdateNote {
       .await?
       .into();
 
-    let id = generate_activity_id(kind.clone(), &context)?;
+    // get object_id
+    let object_id = comment.activity_object_id();
+
+    let id = generate_activity_id(kind.clone(), Some(&object_id), &context)?;
     let note = ApubComment(comment).into_json(&context).await?;
 
     let create_or_update = CreateOrUpdateNote {
diff --git a/crates/apub/activities/src/create_or_update/post.rs b/crates/apub/activities/src/create_or_update/post.rs
index fe423048e8..c270592bc2 100644
--- a/crates/apub/activities/src/create_or_update/post.rs
+++ b/crates/apub/activities/src/create_or_update/post.rs
@@ -46,7 +46,9 @@ impl CreateOrUpdatePage {
     kind: CreateOrUpdateType,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<CreateOrUpdatePage> {
-    let id = generate_activity_id(kind.clone(), context)?;
+    // get object_id
+    let object_id = post.activity_object_id();
+    let id = generate_activity_id(kind.clone(), Some(&object_id), context)?;
     Ok(CreateOrUpdatePage {
       actor: actor.id().clone().into(),
       to: generate_to(community)?,
diff --git a/crates/apub/activities/src/create_or_update/private_message.rs b/crates/apub/activities/src/create_or_update/private_message.rs
index 2b1e78c0e6..1a2adb0a9c 100644
--- a/crates/apub/activities/src/create_or_update/private_message.rs
+++ b/crates/apub/activities/src/create_or_update/private_message.rs
@@ -24,7 +24,11 @@ pub(crate) async fn send_create_or_update_pm(
   let actor: ApubPerson = pm_view.creator.into();
   let recipient: ApubPerson = pm_view.recipient.into();
 
-  let id = generate_activity_id(kind.clone(), &context)?;
+  // get object_id
+  let pm = &pm_view.private_message;
+  let object_id = pm.activity_object_id();
+
+  let id = generate_activity_id(kind.clone(), Some(&object_id), &context)?;
   let create_or_update = CreateOrUpdatePrivateMessage {
     id: id.clone(),
     actor: actor.id().clone().into(),
diff --git a/crates/apub/activities/src/deletion/delete.rs b/crates/apub/activities/src/deletion/delete.rs
index d530f2c50e..29b8e3d818 100644
--- a/crates/apub/activities/src/deletion/delete.rs
+++ b/crates/apub/activities/src/deletion/delete.rs
@@ -1,7 +1,7 @@
 use crate::{
   MOD_ACTION_DEFAULT_REASON,
   deletion::{DeletableObjects, receive_delete_action, verify_delete_activity},
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::{IdOrNestedObject, deletion::delete::Delete},
 };
 use activitypub_federation::{config::Data, kinds::activity::DeleteType, traits::Activity};
@@ -82,7 +82,7 @@ impl Delete {
     with_replies: Option<bool>,
     context: &Data<LemmyContext>,
   ) -> LemmyResult<Delete> {
-    let id = generate_activity_id(DeleteType::Delete, context)?;
+    let id = generate_activity_id_with_object_id(DeleteType::Delete, context)?;
     let cc: Option<Url> = community.map(|c| c.ap_id.clone().into());
     Ok(Delete {
       actor: actor.ap_id.clone().into(),
diff --git a/crates/apub/activities/src/deletion/undo_delete.rs b/crates/apub/activities/src/deletion/undo_delete.rs
index 0c9dea0fe6..decbde1e8e 100644
--- a/crates/apub/activities/src/deletion/undo_delete.rs
+++ b/crates/apub/activities/src/deletion/undo_delete.rs
@@ -1,6 +1,6 @@
 use crate::{
   deletion::{DeletableObjects, receive_delete_action, verify_delete_activity},
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::deletion::{delete::Delete, undo_delete::UndoDelete},
 };
 use activitypub_federation::{config::Data, kinds::activity::UndoType, traits::Activity};
@@ -72,7 +72,7 @@ impl UndoDelete {
       context,
     )?;
 
-    let id = generate_activity_id(UndoType::Undo, context)?;
+    let id = generate_activity_id_with_object_id(UndoType::Undo, context)?;
     let cc: Option<Url> = community.map(|c| c.ap_id.clone().into());
     Ok(UndoDelete {
       actor: actor.ap_id.clone().into(),
diff --git a/crates/apub/activities/src/following/accept.rs b/crates/apub/activities/src/following/accept.rs
index bd8708b236..c90f016c72 100644
--- a/crates/apub/activities/src/following/accept.rs
+++ b/crates/apub/activities/src/following/accept.rs
@@ -1,6 +1,6 @@
 use crate::{
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::following::{accept::AcceptFollow, follow::Follow},
   send_lemmy_activity,
 };
@@ -27,7 +27,7 @@ impl AcceptFollow {
       to: Some([person.id().clone().into()]),
       object: follow,
       kind: AcceptType::Accept,
-      id: generate_activity_id(AcceptType::Accept, context)?,
+      id: generate_activity_id_with_object_id(AcceptType::Accept, context)?,
     };
     let inbox = ActivitySendTargets::to_inbox(person.shared_inbox_or_inbox());
     send_lemmy_activity(context, accept, &target, inbox, true).await
diff --git a/crates/apub/activities/src/following/follow.rs b/crates/apub/activities/src/following/follow.rs
index 486a8a01ff..5a9bc1b992 100644
--- a/crates/apub/activities/src/following/follow.rs
+++ b/crates/apub/activities/src/following/follow.rs
@@ -1,6 +1,6 @@
 use crate::{
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::following::{accept::AcceptFollow, follow::Follow},
   send_lemmy_activity,
 };
@@ -40,7 +40,7 @@ impl Follow {
       object: target.id().clone().into(),
       to: Some([target.id().clone().into()]),
       kind: FollowType::Follow,
-      id: generate_activity_id(FollowType::Follow, context)?,
+      id: generate_activity_id_with_object_id(FollowType::Follow, context)?,
     })
   }
 
diff --git a/crates/apub/activities/src/following/mod.rs b/crates/apub/activities/src/following/mod.rs
index c5a7d715c7..851dded37b 100644
--- a/crates/apub/activities/src/following/mod.rs
+++ b/crates/apub/activities/src/following/mod.rs
@@ -1,4 +1,4 @@
-use super::{generate_activity_id, send_lemmy_activity};
+use super::{generate_activity_id_with_object_id, send_lemmy_activity};
 use crate::protocol::following::{
   accept::AcceptFollow,
   follow::Follow,
@@ -51,7 +51,7 @@ pub async fn send_accept_or_reject_follow(
     to: Some([community.ap_id.clone().into()]),
     object: community.ap_id.into(),
     kind: FollowType::Follow,
-    id: generate_activity_id(FollowType::Follow, context)?,
+    id: generate_activity_id_with_object_id(FollowType::Follow, context)?,
   };
   if accepted {
     AcceptFollow::send(follow, context).await
diff --git a/crates/apub/activities/src/following/reject.rs b/crates/apub/activities/src/following/reject.rs
index 84189ce981..5d379893be 100644
--- a/crates/apub/activities/src/following/reject.rs
+++ b/crates/apub/activities/src/following/reject.rs
@@ -1,7 +1,7 @@
 use super::send_activity_from_user_or_community_or_multi;
 use crate::{
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::following::{follow::Follow, reject::RejectFollow},
 };
 use activitypub_federation::{
@@ -27,7 +27,7 @@ impl RejectFollow {
       to: Some([person.id().clone().into()]),
       object: follow,
       kind: RejectType::Reject,
-      id: generate_activity_id(RejectType::Reject, context)?,
+      id: generate_activity_id_with_object_id(RejectType::Reject, context)?,
     };
     let inbox = ActivitySendTargets::to_inbox(person.shared_inbox_or_inbox());
     send_activity_from_user_or_community_or_multi(context, reject, user_or_community, inbox).await
diff --git a/crates/apub/activities/src/following/undo_follow.rs b/crates/apub/activities/src/following/undo_follow.rs
index 3a776c27d2..c84931f393 100644
--- a/crates/apub/activities/src/following/undo_follow.rs
+++ b/crates/apub/activities/src/following/undo_follow.rs
@@ -1,6 +1,6 @@
 use crate::{
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::following::{follow::Follow, undo_follow::UndoFollow},
   send_lemmy_activity,
 };
@@ -39,7 +39,7 @@ impl UndoFollow {
       to: Some([target.id().clone().into()]),
       object,
       kind: UndoType::Undo,
-      id: generate_activity_id(UndoType::Undo, context)?,
+      id: generate_activity_id_with_object_id(UndoType::Undo, context)?,
     };
     let inbox = ActivitySendTargets::to_inbox(target.shared_inbox_or_inbox());
     send_lemmy_activity(context, undo, actor, inbox, true).await
diff --git a/crates/apub/activities/src/lib.rs b/crates/apub/activities/src/lib.rs
index 4a1c199dde..3ed43678de 100644
--- a/crates/apub/activities/src/lib.rs
+++ b/crates/apub/activities/src/lib.rs
@@ -46,8 +46,9 @@ use lemmy_db_views_site::SiteView;
 use lemmy_diesel_utils::traits::Crud;
 use lemmy_utils::error::{LemmyError, LemmyResult, UntranslatedError};
 use serde::Serialize;
+use sha2::{Digest, Sha256};
 use tracing::info;
-use url::{ParseError, Url};
+use url::Url;
 use uuid::Uuid;
 
 pub mod activity_lists;
@@ -80,34 +81,67 @@ pub(crate) fn check_community_deleted_or_removed(community: &Community) -> Lemmy
   }
 }
 
+/// convenient function for generate_activity_id
+fn generate_activity_id_with_object_id<T>(kind: T, context: &LemmyContext) -> LemmyResult<Url>
+where
+  T: ToString,
+{
+  generate_activity_id::<T>(kind, None, context)
+}
+
 /// Generate a unique ID for an activity, in the format:
 /// `http(s)://example.com/receive/create/202daf0a-1489-45df-8d2e-c8a3173fed36`
-fn generate_activity_id<T>(kind: T, context: &LemmyContext) -> Result<Url, ParseError>
+fn generate_activity_id<T>(
+  kind: T,
+  object_id: Option<&Url>,
+  context: &LemmyContext,
+) -> LemmyResult<Url>
 where
   T: ToString,
 {
-  let id = format!(
-    "{}/activities/{}/{}",
-    &context.settings().get_protocol_and_hostname(),
-    kind.to_string().to_lowercase(),
-    Uuid::new_v4()
-  );
-  Url::parse(&id)
+  let hostname = context.settings().get_protocol_and_hostname();
+  let kind_str = kind.to_string().to_lowercase();
+
+  let uuid_str = if let Some(o) = object_id {
+    let input = format!("{}:{}", kind_str, o.as_str());
+    // hash
+    let mut hasher = Sha256::new();
+    hasher.update(input);
+    let digest = hasher.finalize(); // 32 bytes
+    format!("{:x}", digest)
+  } else {
+    Uuid::new_v4().to_string()
+  };
+
+  let id = format!("{}/activities/{}/{}", hostname, kind_str, uuid_str);
+  Ok(Url::parse(&id)?)
 }
 
 /// like generate_activity_id but also add the inner kind for easier debugging
 fn generate_announce_activity_id(
   inner_kind: &str,
   protocol_and_hostname: &str,
-) -> Result<Url, ParseError> {
+  object_id: Option<&Url>,
+) -> LemmyResult<Url> {
+  let uuid_str = if let Some(o) = object_id {
+    let input = format!("announce:{}", o.as_str());
+    // hash
+    let mut hasher = Sha256::new();
+    hasher.update(input);
+    let digest = hasher.finalize();
+    format!("{:x}", digest)
+  } else {
+    Uuid::new_v4().to_string()
+  };
+
   let id = format!(
     "{}/activities/{}/{}/{}",
     protocol_and_hostname,
     AnnounceType::Announce.to_string().to_lowercase(),
     inner_kind.to_lowercase(),
-    Uuid::new_v4()
+    uuid_str
   );
-  Url::parse(&id)
+  Ok(Url::parse(&id)?)
 }
 
 async fn send_lemmy_activity<A, ActorT>(
diff --git a/crates/apub/activities/src/voting/undo_vote.rs b/crates/apub/activities/src/voting/undo_vote.rs
index 1887ad73d9..9c0dd31e82 100644
--- a/crates/apub/activities/src/voting/undo_vote.rs
+++ b/crates/apub/activities/src/voting/undo_vote.rs
@@ -1,6 +1,6 @@
 use crate::{
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::voting::{undo_vote::UndoVote, vote::Vote},
   voting::{undo_vote_comment, undo_vote_post},
 };
@@ -29,7 +29,7 @@ impl UndoVote {
       actor: actor.id().clone().into(),
       object: vote,
       kind: UndoType::Undo,
-      id: generate_activity_id(UndoType::Undo, context)?,
+      id: generate_activity_id_with_object_id(UndoType::Undo, context)?,
       audience: Some(community.ap_id.clone().into()),
     })
   }
diff --git a/crates/apub/activities/src/voting/vote.rs b/crates/apub/activities/src/voting/vote.rs
index 20287551b3..337aceb471 100644
--- a/crates/apub/activities/src/voting/vote.rs
+++ b/crates/apub/activities/src/voting/vote.rs
@@ -1,6 +1,6 @@
 use crate::{
   check_community_deleted_or_removed,
-  generate_activity_id,
+  generate_activity_id_with_object_id,
   protocol::voting::vote::{Vote, VoteType},
   voting::{undo_vote_comment, undo_vote_post, vote_comment, vote_post},
 };
@@ -31,7 +31,7 @@ impl Vote {
       actor: actor.id().clone().into(),
       object: object_id,
       kind: kind.clone(),
-      id: generate_activity_id(kind, context)?,
+      id: generate_activity_id_with_object_id(kind, context)?,
       audience: Some(community.ap_id.clone().into()),
     })
   }
diff --git a/crates/apub/apub/src/collections/community_outbox.rs b/crates/apub/apub/src/collections/community_outbox.rs
index e1b984c0eb..795511bef7 100644
--- a/crates/apub/apub/src/collections/community_outbox.rs
+++ b/crates/apub/apub/src/collections/community_outbox.rs
@@ -64,8 +64,11 @@ impl Collection for ApubCommunityOutbox {
       )
       .await
       {
-        let announcable = AnnouncableActivities::CreateOrUpdatePost(create);
-        if let Ok(announce) = AnnounceActivity::new(announcable.try_into()?, owner, data) {
+        let announcable = AnnouncableActivities::CreateOrUpdatePost(create.clone());
+        // create id is like https://lemmy.example.com/activities/create/{UUID}
+        if let Ok(announce) =
+          AnnounceActivity::new(announcable.try_into()?, owner, Some(create.id()), data)
+        {
           ordered_items.push(announce);
         }
       }
diff --git a/crates/db_schema/src/impls/comment.rs b/crates/db_schema/src/impls/comment.rs
index 034427e847..2faad1a493 100644
--- a/crates/db_schema/src/impls/comment.rs
+++ b/crates/db_schema/src/impls/comment.rs
@@ -320,6 +320,14 @@ impl Comment {
       .await
       .with_lemmy_type(LemmyErrorType::NotFound)
   }
+
+  /// Return the comment's ap_id with a timestamp fragment appended.
+  pub fn activity_object_id(&self) -> Url {
+    let timestamp = self.updated_at.unwrap_or(self.published_at);
+    let mut object_id = (*self.ap_id.0).clone();
+    object_id.set_fragment(Some(&timestamp.to_rfc3339()));
+    object_id
+  }
 }
 
 impl Crud for Comment {
diff --git a/crates/db_schema/src/impls/post.rs b/crates/db_schema/src/impls/post.rs
index 1dc4742c95..e980c9f015 100644
--- a/crates/db_schema/src/impls/post.rs
+++ b/crates/db_schema/src/impls/post.rs
@@ -343,6 +343,14 @@ impl Post {
     }
     Ok(())
   }
+
+  /// Return the post's ap_id with a timestamp fragment appended.
+  pub fn activity_object_id(&self) -> Url {
+    let timestamp = self.updated_at.unwrap_or(self.published_at);
+    let mut object_id = (*self.ap_id.0).clone();
+    object_id.set_fragment(Some(&timestamp.to_rfc3339()));
+    object_id
+  }
 }
 
 impl Likeable for PostActions {
diff --git a/crates/db_schema/src/impls/private_message.rs b/crates/db_schema/src/impls/private_message.rs
index c1c81fe9e4..394ed1d653 100644
--- a/crates/db_schema/src/impls/private_message.rs
+++ b/crates/db_schema/src/impls/private_message.rs
@@ -109,6 +109,14 @@ impl PrivateMessage {
       self.deleted_by_recipient = false;
     }
   }
+
+  /// Return the private message's ap_id with a timestamp fragment appended.
+  pub fn activity_object_id(&self) -> Url {
+    let timestamp = self.updated_at.unwrap_or(self.published_at);
+    let mut object_id = (*self.ap_id.0).clone();
+    object_id.set_fragment(Some(&timestamp.to_rfc3339()));
+    object_id
+  }
 }
 
 #[cfg(test)]