Policy needed for action on the following types of calls

Someone sent me a mail at time X from address Y and I have not received it. Can you check the logs?

I sent an email to X at time Y and they have not received it. Can you check the logs and make sure it was sent?

Overhead of checking logs is considerable both in human and machine time (the latter might improve, see ?maillogs). A policy of "we will not investigate until 12 hours have passed" or similar might be sensible (timing adjusted to be suitable and in line with the practical delays of SMTP messages)