Hi @rafael9908 ,
According to your description, please confirm some questions to narrow down the issue to client side or server side.
Please clarify whether the issue happens to all users or specific users.
Please try to send mails via OWA or Online mode. If the problem no longer occurs, it is related to the client side.
For client side, you can follow below steps:
1.Check if “Send Immediately” is enabled in Advanced settings.
2.Recreate user profile.
3.Please login on the user’s mailbox on another normal machine to test.
For server side, you can follow below steps:
- Make sure that the server has the latest cumulative and security updates installed.
2.Please watch the event logs for any warnings or errors and consider starting Performance Monitor and watching key performance metrics.
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