This issue happens because, starting September 26, 2025, Render’s free tier blocks outbound traffic on traditional SMTP ports 25, 465, and 587.

Emails fail with a 500 Internal Server Error even if credentials and configuration are correct. To fix this, use port 2525, which remains open on the free tier and is supported by SMTP2GO.

After switching to port 2525, email sending works normally without changing any other part of your setup. No upgrade required unless you want to use standard ports.