Dtrace excerpt of MigratorServer shows:
{CSaveset2::ExtractMsgBestBody:#2241} _com_error exception: [Unspecified error (0x80004005)]
{CSaveset2::ExtractMsgBestBody} (Exit) Status: [Unspecified error (0x80004005)]
Email size exceeds the limit in the mailbox
Increase the MaxSendSize and MaxReceiveSize of the mailbox.
More Information:
Configure message size limits for a mailbox
https://technet.microsoft.com/en-us/library/bb124708(v=exchg.160).aspx
‘Export to original mailbox’ completes partially.