Mailcatcher vs. smtp4dev
A solid open-source, self-hosted SMTP test server with raw protocol-level logging — no team features or hosting included.
| Feature | Mailcatcher | smtp4dev |
|---|---|---|
Deployment | Hosted SaaS | Self-hosted (Docker, Windows service, or binary) |
Setup | Point your SMTP settings at us | Install, run, and keep the server up |
Team accounts & permissions | Yes | No |
Shared access without exposing your network Remote access means running your own reverse proxy or tunnel | Yes | No |
Multiple isolated projects | Unlimited | One shared inbox per instance |
HTML/text preview, headers & attachments | Yes | Yes |
Raw SMTP session/protocol logs Useful when you're debugging the SMTP conversation itself, not just the email content | No | Yes |
Open source / full control Free, self-hosted, cross-platform | No | Yes |
What is smtp4dev?
smtp4dev is a free, open-source SMTP test server built on .NET. It runs cross-platform (Docker, Windows, Linux, macOS) and catches outgoing mail for local inspection, alongside some IMAP retrieval and message-relay options.
Where smtp4dev shines
Beyond the usual HTML/text preview, smtp4dev exposes the raw SMTP session log — the actual protocol exchange between your app and the server. That's a real advantage if you're debugging an SMTP client implementation or a tricky connection issue, rather than just checking what an email looks like.
Where Mailcatcher differs
smtp4dev, like most self-hosted catchers, gives you a single shared inbox per instance with no accounts or permissions — fine for one developer, awkward for a team. Someone still has to run the server, keep it updated, and expose it if anyone else needs access.
Mailcatcher trades that raw protocol-level detail for a hosted, multi-project setup: unlimited projects, team accounts with permissions, and nothing to install or maintain.
Which should you choose?
If you're troubleshooting SMTP protocol behavior itself and want full control over a self-hosted tool, smtp4dev is a good, actively developed option. If you want your team to share and organize captured emails across projects without running infrastructure, Mailcatcher is the more direct fit.