feat(service): Add Stalwart mail server

[vlad6tz]

Changes

• Added Stalwart mail server as a one-click service for Coolify. It's a complete, open-source mail server with SMTP, IMAP, POP3, JMAP support and a web UI. Includes all necessary mail ports and persistent storage.

Issues

• Rate limiting issue where Stalwart blocks Traefik proxy connections, causing recurring "bad gateway" errors. Solution includes whitelisting Docker network in Stalwart's IP allowlist.

Category

• Bug fix
• Improvement
• New feature
• Adding new one click service
• Fixing or updating existing one click service

Preview

AI Assistance

• AI was NOT used to create this PR
• AI was used (please describe below)

If AI was used:

• Tools used: Codex
• How extensively: Used for docker-compose optimization

Testing

Verified all mail protocols working (SMTP, IMAP, POP3), DKIM signing valid, SPF and DMARC passing authentication checks, reverse proxy routing stable, persistent storage functioning correctly, and rate limiting issue resolved with Docker network whitelist config.

Contributor Agreement

Important

• I have read and understood the contributor guidelines. If I have failed to follow any guideline, I understand that this PR may be closed without review.
• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate.
• I have tested all the changes thoroughly with a local development instance of Coolify and I am confident that they will work as expected when a maintainer tests them.