Thank you for posting your inquiry.
We have tested the same scenario at our end with test office 365 account having around 300 messages and it didn’t raise any exception. Can you please share further details about the amount of data in the inbox and if it contains only message replies or there are some other type of messages as well such as appointment replies? Also, please make sure that you are using the latest version of the API i.e. Aspose.Email for .NET 6.1.0.