SupabaseS
Supabase•5w ago
Kurt

Unable to Send Auth Emails via Sender.net SMTP – Unexpected Failure

gm gm,

I am trying to configure Sender.net as a custom SMTP provider for authentication emails in my project, but I am unable to send any emails.

Settings used in Supabase:

  • Sender email: no-reply@example.com (verified domain)
  • Sender name: Example Auth
  • SMTP host: smtp.sender.net
  • SMTP ports tried: 587 (TLS/STARTTLS), 465 (TLS), 2525
  • Username: smtp-user
  • Password: correct SMTP password
  • Secure: TLS/STARTTLS
Observed errors when sending test emails via Supabase:

{"code":"unexpected_failure","message":"Error sending confirmation email"}


or sometimes

{"code":"over_email_send_rate_limit","message":"email rate limit exceeded"}


Notes / Debug info:

  • The same SMTP credentials work perfectly in a standalone Node.js test script from a local machine.
  • Sender.net logs show no failed auth attempts when Supabase tries to send.
  • Port 465 times out, port 587 returns "unexpected_failure", and port 2525 also fails.
  • The From email is verified and exists in MX; SPF, DKIM, and DMARC are correctly set.
  • This suggests the connection may be blocked or failing from the Supabase cloud environment rather than an SMTP credential issue.
Could anyone advise how to debug SMTP connectivity from Supabase cloud, or a recommended workaround for using Sender.net as a custom SMTP provider for auth emails?

Thanks!
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