During a recent project involving the migration of emails from an on-premises Exchange server to Office 365, I utilized a third-party tool known as Avepoint. Throughout this process, I encountered several peculiar issues that required thorough investigation, despite their seemingly straightforward nature. Recognizing the potential value of sharing these experiences, I aim to provide insights for others who may encounter similar challenges.
Although the email migration was completed successfully without encountering any error messages, a notable incongruity emerged during the comparison of source and destination mailbox sizes. Notably, this anomaly was observed only among select users, further underscoring the complexity of the situation. Following were the issues I encountered:
- The inconsistency in mailbox sizes between the source and destination for specific users was attributed to the presence of a retention policy that resulted in the deletion of messages. This policy significantly influenced the observed difference in sizes encountered during the migration procedure. You can use the following command by connecting to exchange online power shell and check the retention of all mailboxes and see if any of the mailboxes have any thing out of ordinary. Get-Mailbox | ft displayname, retentionpolicy
- Another issue encountered during a separate client’s email migration pertained to their send and receive size limits, which inadvertently led to certain emails failing to migrate. Remarkably, despite this obstacle, the migration tool did not generate any error notifications. You can execute the following by connecting to exchange online power shell to check the send / receive size limits of all mailboxes and up it if need be which is what I did to fix this issue. Get-Mailbox | ft displayname, maxreceivesize, maxreceivesize
Salman Tariq
SalmanTechBlogs 
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