A lightweight Windows desktop application for personalized bulk e-mail campaigns.
Import your recipients, compose a message with merge fields, configure one or more SMTP servers, and send — with full start / pause / resume / stop control over the background sending job.
- Screenshots
- Features
- Requirements
- Getting started (users)
- Building from source
- Running the tests
- Usage guide
- File formats
- Personalization tokens
- Project structure
- Contributing
- License
- Acknowledgements
| Recipients | Mail Content | Options |
|---|---|---|
 |
 |
 |
- Personalized mass mailing — merge recipient fields (name, company, etc.) into the subject and body with simple
<=Token>placeholders. - Three delivery modes:
- SMTP — modern, secure delivery via MailKit, with implicit SSL/TLS and STARTTLS support and SMTP authentication.
- MAPI — hand the message to the local mail client. Note that this is discontinued on Windows 11!
- Direct — deliver straight to the recipient's mail server via DNS MX lookup.
- Multiple SMTP servers — distribute a campaign across several servers, with per-server message limits and automatic fail-over to the next enabled server.
- Robust send-job control — safely start, pause, resume, and stop the background sending thread at any time (backed by a proper thread-synchronization gate, not a busy-wait).
- Throttling — limit messages per connection and insert configurable delays between batches. Note: Depending on your mail provider, it can be necessary to limit the throughput when sending mails. There are email providers that are known to allow only 60 mail per hour! Even if you are hosting a server yourself, it is a good idea to throttle so you dont get blacklistet by relays or receivers mail providers.
- Recipient filtering — name, e-mail, domain blacklists, a no-send list, duplicate detection, and e-mail-address validation.
- Automatic retry of failed recipients after a configurable interval.
- Import & export address books in vertical-text, comma/tab-delimited, XML, and e-mail-only formats.
- HTML or plain-text bodies with a live preview tab.
- Attachments support.
| Operating system | Windows (Windows Forms, MAPI, and the WebBrowser preview control are Windows-only) |
| Runtime | .NET Framework 4.8 |
| To build | Visual Studio 2022 or the .NET Framework 4.8 build tools (MSBuild) |
| Bundled dependencies | MailKit 4.17 and MimeKit 4.17 (restored automatically from NuGet) |
⚠️ Responsible use. This tool sends bulk e-mail. Only mail people who have agreed to hear from you, honor unsubscribe requests, and comply with anti-spam laws such as the GDPR, the CAN-SPAM Act, and your provider's terms of service.
- Download the latest build from the Releases page (or build it yourself — see below).
- Make sure .NET Framework 4.8 is installed (it ships with Windows 10 1903+ and Windows 11).
- Run
EmailSender.exe.
Prefer to build it yourself? Read on.
Clone the repository:
git clone https://github.com/Thomas-Mielke-Software/EmailSender.git
cd EmailSender- Open
EmailSender.slnin Visual Studio 2022. - Visual Studio restores the NuGet packages automatically on first load.
- Select the Debug or Release configuration and press F6 (Build) or F5 (Run).
From a Developer Command Prompt / Developer PowerShell for VS:
# Restore NuGet packages, then build the whole solution
msbuild EmailSender.sln /t:Restore
msbuild EmailSender.sln /p:Configuration=ReleaseThe application is produced at:
EmailSender/bin/Release/EmailSender.exe
💡 To build only the application (skipping the test project):
msbuild EmailSender/EmailSender.csproj /t:Restore;Build /p:Configuration=Release
The Windows installer is built with Inno Setup 6 (6.3 or newer). The bump-version.ps1 script raises the version in AssemblyInfo.cs, mirrors it into EmailSender.iss, builds the Release output, compiles the installer into Setup/, and creates a git commit + tag vX.Y.Z:
# Increase the version (major | minor | patch), build, package, commit + tag
.\bump-version.ps1 -Part patch
# ...and push the commit and tag as well
.\bump-version.ps1 -Part minor -Push
# Preview the version change only (no write, build or git)
.\bump-version.ps1 -Part patch -DryRunBecause EmailSender is an AnyCPU .NET Framework application, a single installer covers x86, x64 and ARM64 — the managed binaries are architecture-neutral, so no per-architecture build is needed. The produced executables are not signed unless a sign tool is enabled (the SignTool line in EmailSender.iss); configure your own in the Inno Setup IDE.
The UnitTests project uses NUnit 3 with the NUnit3TestAdapter and the Microsoft.NET.Test.SDK.
Open Test ▸ Test Explorer and run all tests (Ctrl+R, A). The tests run on an STA thread (required by the form's WebBrowser control) automatically.
# Build the test project (this also builds the app it references)
msbuild UnitTests/UnitTests.csproj /t:Restore;Build /p:Configuration=Debug
# Run the tests with VSTest
vstest.console.exe UnitTests/bin/Debug/UnitTests.dll `
/TestAdapterPath:"$env:USERPROFILE\.nuget\packages\nunit3testadapter\4.5.0\build\net462" `
/Platform:x86Use Recipients ▸ Import External File… and pick the matching file type. Imported contacts appear in the Recipients tab, where you can check/uncheck individuals, edit them, or remove duplicates. See File formats for the exact layouts.
On the Mail Content tab, fill in the Sender email, Sender name, Reply to, Subject, and body, and choose the Priority, Format (text/plain or text/html), and Encoding. Insert personalization tokens (via the Compose Email menu) to merge per-recipient data. Add files on the Attachment tab, and switch the body's Preview sub-tab to render the result.
Open View ▸ Options to choose the delivery mode (SMTP, MAPI, or Direct), define one or more SMTP servers (host, port, SSL/TLS or STARTTLS, credentials, per-server limits), set throttling and retry behavior, and manage the recipient filters.
💡 Note that MAPI is discontinued on Windows 11! This option is only available in case you use older and no longer supported versions of Windows (not recommended) or Wine environments (not even tested).
Drive the campaign from the toolbar or the Send menu:
| Action | What it does |
|---|---|
| ▶ Start | Begins (or resumes) sending the checked recipients on a background thread. |
| ⏸ Pause | Cleanly halts after the current message; queued recipients are marked Paused. |
| ▶ Start (while paused) | Resumes exactly where it left off. |
| ⏹ Stop | Aborts the job; the UI returns to idle. |
The status bar tracks success / failure / total counts live, and every action is written to the Log tab.
EmailSender imports and exports the following layouts.
Contacts are separated by at least one blank line; each labeled field is on its own line. Lines whose label is not recognized are ignored. Labels are case-sensitive.
1. Acme Corporation
Address: 42 Wallaby Way, Sydney
Phone: +1 604 1234 5678
Fax: +1 604 1234 5679
E-mail: jane@acme.com
Website: www.acme.com
Contact: Jane Doe
Memo: Preferred customer
| Label | Maps to |
|---|---|
E-mail: |
E-mail address |
Contact: |
Recipient name |
Address: / Phone: / Fax: / Website: |
Stored with the contact |
One contact per line, fields separated by a comma or a tab.
The application's native, round-trippable address-book format.
A plain list of one e-mail address per line — handy for quick blasts.
Drop these placeholders into the Subject or Body; they are replaced per recipient at send time. (The Compose Email menu inserts them for you.)
| Token | Replaced with |
|---|---|
<=Email> |
Recipient e-mail address |
<=Name> |
Recipient name |
<=Company> |
Recipient company |
<=Status> |
Recipient status field |
<=Memo> |
Recipient memo field |
<=FromEmail> |
Sender e-mail |
<=FromName> |
Sender name |
<=ReplyEmail> |
Reply-to address |
<=Time> |
Current date/time at send |
Example
Subject: <=Name>, your Acme order has shipped
Hello <=Name>,
Thank you for being a valued customer at <=Company>.
This message was sent on <=Time>.
EmailSender.sln Visual Studio solution
├─ EmailSender/ The Windows Forms application
│ ├─ FrmMain.cs Main window, recipient list, and send-job state machine
│ ├─ ClassSmtp.cs SMTP / MailKit delivery
│ ├─ ClassSettings.cs Application options & SMTP server definitions
│ ├─ ClassFile.cs Address book model + import/export
│ ├─ ExternalData.cs External-data helpers
│ ├─ MapiApi.cs MAPI integration
│ └─ Image/ Toolbar and status icons
├─ UnitTests/ NUnit 3 test project
├─ EmailSender.iss Inno Setup script (universal x86/x64/ARM64 installer)
├─ bump-version.ps1 Bumps the version, builds Release, compiles the installer
└─ Doc/ Change log, release notes, screenshots
Issues and pull requests are welcome. To get going:
- Fork the repo and create a feature branch.
- Build the solution and make sure the tests pass (see Running the tests). (I.t.m. there is only one test, more tests appreciated!)
- Keep changes focused and match the surrounding code style.
- Open a pull request describing the change and the motivation.
Please don't commit build output (bin/, obj/) or IDE state — the included .gitignore already excludes them.
EmailSender is free software, released under the GNU General Public License v2. See the LICENSE file for the full text. It is distributed in the hope that it will be useful, but without any warranty.
- Originally published on SourceForge as a .NET Framework 2.0 application.
- Modernized by Thomas Mielke for this repository: migrated to .NET Framework 4.8, the legacy LumiSoft.Net SMTP stack replaced with MailKit / MimeKit for SSL/TLS and STARTTLS support, the background send-job state machine hardened, and the test project brought up to NUnit 3.