Fixing Discourse Email Delivery: Complete SMTP & Deliverability Troubleshooting Guide

Direct Answer: When Discourse emails fail to send, the root cause is almost always either port 25/587 outbound firewall blocking by your VPS provider, invalid SMTP authentication credentials in app.yml, or missing SPF, DKIM, and DMARC DNS records causing recipients to drop messages into spam.

Diagnostic Step 1: Check Internal Discourse Email Logs

Before changing server settings, inspect the internal error trace provided by Discourse:

1. Navigate to /admin/email/logs.
2. Inspect the Skipped, Bounced, and Rejected tabs to see if emails are being blocked by spam filters.
3. Visit /admin/logs/staff_action_logs to check for SMTP connection timeout exceptions.

Diagnostic Step 2: Test Outbound SMTP Port Connectivity

Major cloud providers (Hetzner, DigitalOcean, AWS, Linode) block outbound port 25 by default to prevent spam. Discourse should always connect via port 587 (STARTTLS). Test connectivity from inside your VPS:

Step 3: Correct DNS Authentication (SPF, DKIM & DMARC)

In 2026, Gmail and Yahoo enforce strict email authentication rules. Unauthenticated emails are rejected outright:

• SPF Record (TXT): Add v=spf1 include:amazonses.com ~all (replace with your provider's include string).
• DKIM (CNAME or TXT): Copy the exact public cryptographic keys generated in your email provider console into your DNS manager (e.g. Cloudflare).
• DMARC Record (TXT): Create a TXT record for _dmarc.yourdomain.com with value v=DMARC1; p=quarantine; rua=mailto:[email protected].

Recommended Email Providers for Discourse

• Amazon SES: Most affordable ($0.10 per 1,000 emails), rock-solid reliability once moved out of sandbox mode.
• Postmark: Highest delivery speeds and cleanest interface; best for communities with high transaction velocity.
• Microsoft 365 / Google Workspace: Suitable only for low-volume private forums (daily sending limits apply).