You can troubleshoot delivery problems for messages using Email Log Search.
Before you start, make sure the user has completed these recommended steps.
From a G Suite user to a non-G Suite email provider—Confirm the message appears in Email Log Search (and therefore was successfully sent). If not, trace the message starting with the sender. If the message does appear in logs, you will need to check with the recipient domain for issues.
From a G Suite user to another G Suite user—Ensure the message appears in Email Log Search. If the message does not appear, check the MX records of the recipient domain.
From a non-G Suite email provider to a G Suite user—Look for the message in Email Log Search. If it's not there, contact the sender. Have them review filters and firewall settings.
Confirm post-delivery message status
If you have confirmed the delivery of a message to a user within your domain, Post-delivery message status can assist in locating the message in the user’s mailbox. Expand the output to identify the current location of the message or if it has been deleted.
Older than 30 days—If the message was received more than 30 days ago, message delivery logs won’t be available. By selecting this date range, you can search with a message ID and the recipient details to view the status of the message in a user’s mailbox.
Note: If the message triggers any compliance rules you set, this information appears in the message details under Matched rules.
Evaluate Email Log Search results
Also consider these general tips when evaluating Email Log Search results:
If a message known to exist and sent to a known user doesn't appear in the logs, the message likely never made it to the Google network. Examine the route leading to Google for the failure. Contact the sending or recipient domain to troubleshoot the issue.
If a delayed message shows a Google transit time of less than 10 minutes, any observed delay is likely caused by a third-party provider. Try using the message header analyzer to examine the route a message took and determine where the message was delayed.
Messages bounced with "The email account that you tried to reach does not exist" won't show in the logs unless you forward the message to a catch-all or legacy server.