Why Your SMTP Relay Emails Are Getting Rejected

Set up your relay credentials correctly but emails are still bouncing or getting rejected? Here's how to actually diagnose it, instead of guessing.

Step 1: Read the Actual Bounce Message

Every rejection comes with a reason, usually in the bounce email or your sending app's error log. The exact wording tells you which of the following it is — don't skip straight to troubleshooting everything at once.

"Authentication failed"

• You're using the wrong password — double check you're using the relay account's password, not your RepublicNodes login.
• Your username should be the full relay email/username shown on your service page, not a shortened version.
• Make sure your app is actually configured to authenticate (SMTPAuth = true or equivalent) — some libraries default to no-auth and silently fail differently depending on the platform.

"Relaying denied" or "Not authorized to send as this address"

• The From address your app is sending as must match what your relay account is actually authorized to send as. Sending "from" a domain/address your relay wasn't configured for is blocked by design — this exact restriction is what stops the relay from being abused as an open spam relay for everyone else's traffic too.

"Rate limit exceeded" or "Too many messages"

• Your relay tier has a sending limit per hour/day — check your plan's page for the exact number. If you're legitimately sending more than that, a higher relay tier raises the ceiling.
• A sudden burst of retries from your app (a bug causing the same email to resend repeatedly) can also trigger this — check your app's logs for unexpected duplicate sends before assuming you need a bigger plan.

Message Sends Successfully But Never Arrives

This usually isn't an SMTP connection problem at all — it's deliverability. Check:

• Whether your domain has correct SPF, DKIM, and DMARC records — missing or broken DKIM in particular causes silent spam-foldering rather than an outright bounce.
• The recipient's own spam folder, before assuming it vanished entirely.

Connection Timeouts / Can't Connect At All

• Double-check the exact hostname and port from your service page — a typo here fails at the connection level before authentication is even attempted.
• Some networks/hosting providers block outbound port 25 by default (a common anti-spam measure across the industry) — if you're connecting from another server, try port 587 (STARTTLS) instead, which is rarely blocked.

Still Stuck?

Open a support ticket with the exact error message, the from-address you're sending as, and roughly when it happened — that's enough for us to check the relay logs on our side and tell you definitively what's actually happening, rather than guessing from a vague "it's not working."