When a user enables out-of-office (OOO) settings while working on a local replica of their mail file and does not replicate with the server before logging out, it can cause issues. The OOO status will not be reflected on the server's mail file while the user is away.
When the user returns to the office and replicates with the server, the OOO will then be enabled. However, as the time set for the OOO to end has already passed, the first email they receive will disable the OOO notification and send a "welcome back" message without notifying anyone of their absence.
To prevent this situation, please advise the end user to replicate their local mail file with the server after enabling the out of office setting, and before logging out.