Email & SMTP · 1 min read
Troubleshooting SMTP Email Delivery Issues
Why SMTP emails fail
SMTP providers only send mail from sender identities they've verified. Most failures happen because:
- The From address isn't verified with your SMTP provider
- The From address differs from the account configured in your SMTP settings
- The sending domain isn't verified or authenticated (SPF, DKIM)
- The provider's security rules block the login or the message
In many cases, correcting the sender email fixes the problem right away.
Check your sender email
- Go to Settings → Email Services → SMTP Service and note the email address on the connected service.
- Make sure the From email in your campaigns, workflows and templates matches that address or a sender your provider has verified.
- If you use several From addresses, verify each one with your provider.
Read the error in Conversations
Open the contact's conversation and hover over or click the failed email. The error text from the provider usually says what's wrong, for example "sender not authorized" or "authentication failed".
Common fixes
- Authentication failed: re-enter the username and password (or app password) for the SMTP service.
- Sender not verified: verify the address or domain in your SMTP provider's dashboard.
- Connection refused or timed out: check the host, port and encryption settings.
- Daily limit reached: your provider caps how much you can send. Wait for the limit to reset or raise it with the provider.
Best practices
- Authenticate your sending domain with SPF, DKIM and DMARC.
- Send a test email after any change to your SMTP settings.