This page covers the most common email delivery problems and how to resolve them.
Emails Not Sending
Work through these steps in order before digging into provider-specific errors.
- Confirm the mailer is configured at
WP Admin > NimblyMail > Settings > Connection. An unconfigured mailer falls back to PHP Mail, which many hosts block. - Send a test email at
WP Admin > NimblyMail > Tools > Email Testerto isolate whether the problem is with the mailer or with a specific email trigger. - Verify that Do Not Send is not enabled at
WP Admin > NimblyMail > Settings > Misc. When this toggle is on, no emails are dispatched. - Enable Debug Mode at
WP Admin > NimblyMail > Settings > Misc > Debug Modeto capture the full SMTP protocol conversation on the next send attempt. - Check
WP Admin > NimblyMail > Email Logsfor error messages on recent failed entries.
SMTP Connection Errors
| Error | Likely Cause | Resolution |
|---|---|---|
| Connection timed out | Host or port is wrong, or firewall is blocking the connection | Verify the hostname and port. Ask your host whether outbound connections on port 587 or 465 are permitted. |
| Authentication failed | Wrong username or password, or 2FA is active on the account | Double-check credentials. If the account has two-factor authentication enabled, generate and use an app-specific password. |
| Certificate verification failed | SSL/TLS certificate on the SMTP server cannot be verified | Enable Auto TLS if available, or try switching the encryption setting between TLS and SSL. |
| Could not connect to SMTP host | Hostname is incorrect or the host is unreachable | Verify the hostname exactly as given by your provider. Contact your host to confirm outbound SMTP is not blocked. |
Gmail OAuth Issues
| Error | Resolution |
|---|---|
redirect_uri_mismatch |
The authorized redirect URI in Google Cloud Console must match the callback URL shown in NimblyMail exactly, including the protocol and trailing slash. |
| Token expired | NimblyMail refreshes OAuth tokens automatically. If the refresh fails, disconnect the Gmail connection at WP Admin > NimblyMail > Settings > Connection and reconnect by going through the OAuth flow again. |
| Access denied | Confirm that the Gmail API is enabled in your Google Cloud Console project under APIs & Services > Enabled APIs. |
Amazon SES Issues
| Error | Resolution |
|---|---|
MessageRejected |
The sending domain or From email address has not been verified in SES. Complete domain or email verification in the AWS SES console. |
| Emails only reach verified addresses | Your SES account is in sandbox mode. New accounts start in sandbox, where you can only send to verified addresses. Submit a request for production access in the AWS SES console. |
| Invalid region | The configured region must match the AWS region where your SES sending identities are set up. Check the region selector in your SES console URL. |
Resend / SendLayer Issues
| Error | Resolution |
|---|---|
| Invalid API key | Copy the key again from your provider dashboard. Keys are case-sensitive and must be copied in full. |
| Domain not verified | Complete DNS record verification in your provider’s dashboard. DNS changes can take up to 48 hours to propagate. |
| Rate limited | You have exceeded your plan’s sending limits. Check your provider’s dashboard for current usage and upgrade if needed. |
Debug Mode
Enable Debug Mode at WP Admin > NimblyMail > Settings > Misc > Debug Mode to capture the full SMTP protocol conversation for each send attempt. The debug output appears in the Details tab of the email log entry for that message.
Debug output includes every command and response exchanged between WordPress and the mail server. Credentials (username and password) are automatically redacted before the log is saved.
Disable Debug Mode once you have gathered the information you need. Debug logs are retained for the number of days configured in Debug Log Retention (Days) and then automatically deleted.
Getting Help
Before reaching out for support:
- Check the email log detail view for the specific error message returned by the mailer.
- Enable Debug Mode and send a test email to capture the full SMTP conversation.
- Verify that your hosting provider permits outbound email connections on your chosen port.
- Try switching to a different mailer at
WP Admin > NimblyMail > Settings > Connectionto determine whether the problem is provider-specific.