Check the address and routing order
Start with the recipient address shown in the message and compare its spelling, subdomain, and punctuation with the configured mailbox or alias. Routing uses the address as received; a typo or a different domain can make an otherwise familiar name resolve differently.
The catch-all is evaluated after exact mailboxes and aliases. If a matching address exists but the message still goes elsewhere, check that the mailbox is active, the alias points to the expected destination, and the incoming domain is the one configured for the account. Do not create a broad catch-all just to conceal a missing address.
Test the intended recipient path
Send a test from an external address to the exact mailbox address, then test the alias separately. Check the destination inbox and any configured forwarding. Keep the message identifier and time if the actual route differs from the configuration.
If the exact address, alias, and catch-all are all involved, review them together because the first matching rule determines delivery. Remove stale or overlapping aliases only after confirming that no user or workflow depends on them. A narrow explicit address is easier to audit than a catch-all receiving everything.