Outlook Keeps Re-Downloading the Same Emails!

I recently had a customer that upgraded from Microsoft Outlook 2007 (same for Outlook 2003) to Outlook 2016.  Once the software upgrade was complete, Outlook 2016 repeatedly tried to re-download all 18,000 of his emails, although unsuccessfully multiple times!  Yes, all 18,000 of them; you read that right.  As you may know, with new versions of software, come improvements.  The Outlook 2007 limit for how large the email file (not mailbox) container holding all his emails was only 2GB although the newer Outlook 2016 limit is 50GB.  Since he was re-using the Outlook 2007 email file, when he upgraded to Outlook 2016, the old 2GB size limited carried over since it was a file limitation, not a software limitation.  In order to solve the 2GB limitation, I had to create a completely new email file for him using Outlook 2016.  Among other things, this required recreating, from scratch, his Outlook 2016 email account.  As an FYI, I did not find anything about how to solve this problem on the Web.  If you are experiencing this problem and would like help, please contact me to schedule an appointment!  It's an easy fix, but very involved in getting it right.