Thank you for writing to Aspose Support team.
We have tested this issue at our end with the latest version of Aspose.Email for .NET 6.3.0 and were not able to face any issue. The issue was tested with around 1000+ emails and all the emails were fetched successfully without raising an exception. Enabling ImapClient Activity logging may provide some information about the nature of problem. Please try it and share the output log file with us if you face the issue again.