The underlying connection was closed

​​​​​​The underlying connection was closed: This error message may occur when migrating a large item (containing large attachments, for instance). The Destination system will keep a connection open only for so long, after which the connection will be closed (timeout).


If the referenced server's configuration is under your control:

  • Increase the connection timeout for incoming data transfers (see the sample screenshot below for IIS, use a value larger than 120).
  • Increase the size limit of items that can be created through the API.

Once the mailbox migration is completed:

To access the dialog below follow the next steps.

  1. Go to the Exchange Server.
  2. Start the IIS manager (run -> inetmgr.exe)
  3. Browse to the default website or the Exchange website.
  4. Find the website under which it is located.
  5. Right-click Manage Website, select Advanced Settings, and expand Connection Limits.


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