Understanding Failure Alerts
A failure alert means your WordPress site just tried to send an email and couldn't. Someone's order confirmation, password reset, or form enquiry did not go out.
What exactly happened
WordPress fires an internal event called wp_mail_failed whenever wp_mail() can't hand an email to the mailer. The WP Mail Tester plugin listens for that event and reports it to us instantly — the alert reaches you within about a minute of the failure, usually before anyone else notices.
Each alert includes the error message, the intended recipient, the subject line, and which SMTP plugin was active. Recent failures are also listed on your dashboard.
Common error messages, decoded
| Error contains… | Usual meaning | Fix |
|---|---|---|
Could not authenticate / 535 | SMTP username/password or API key is wrong or expired | Re-enter credentials in your SMTP plugin; regenerate the provider API key |
Connection refused / timed out | Host can't reach the mail server — port blocked or provider down | Ask your host about outbound SMTP ports; check the provider's status page |
550 / Sender address rejected | From address isn't verified with the provider | Verify the sending domain/address in your provider dashboard |
Daily sending limit / quota | You've hit the provider's or host's sending cap | Upgrade the provider plan, or find what's sending so much (a hacked site sends spam!) |
Invalid address | A malformed recipient — often a form-validation gap | Usually harmless one-offs; recurring ones point at a specific form |
What to do when you get one
- Read the error — the table above covers the common cases
- Check your SMTP plugin's settings/logs on the affected site
- Run a test from Tools → WP Mail Tester to confirm whether sending is fully down or the failure was a one-off
- If sending is down and the error is unclear — contact us, or the Expert Fix handles it done-for-you
Alert behaviour
- Failures are always recorded for connected sites (visible on your dashboard)
- Instant alerts (email + Telegram/Slack) are a paid-plan feature
- Alerts are rate-limited to one per site per 30 minutes — a burst of failures becomes one alert that mentions the count, not thirty emails
- A related alert, configuration change, fires when your SMTP plugin, From address, or mailer settings change — the leading cause of failures. One per site per 6 hours.
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