How to fix a fallback-domain send

The primary sending domain failed and Lumail retried through a fallback domain. Fix the primary.

You got Email used fallback domain or Workflow email used fallback domain. The recipient got mail, but not from the From domain you configured. Lumail retried through a fallback you set on Domains.

The display name and local part stay the same; only the domain changes (Melvyn <[email protected]> → Melvyn <[email protected]>).

What to change

Open Domains. The alert names the primary host and the fallback that was used.
Fix the primary domain — usually MAIL FROM, SES identity, or DKIM. Use the error sentence in the notification:
Verify the primary domain. New sends stop using the cached fallback (Lumail caches a successful fallback for 10 minutes for that org + primary).
If no fallback is configured and you want this safety net, set Fallback priority on a second verified domain.

Fallback does not fix account-level pause, quota, or a missing configuration set.

Email Domains — fallback priorities
How to fix a failed send

PreviousHow to fix a failed send NextHow to fix an invalid email parameter