As far as I know due to the page property size the maximum size of any distribution list cannot exceed 8KB.
We've been using very some large distribution lists for years on Exchange 2010. But all of a sudden as soon as we've upgraded to Exchange 2013 I I receive a "This distribution list has reached the maximum size for your network e-mail server" error message when you try to add many items to a contact distribution list in Outlook (ref: KB 238569)
The distribution list contains 2500 contacts with name and email only.
That should not be a problem in Outlook 2013.
Can you help me to understand?