Hi,
I've upgraded Exchange 2013 to 2019 and everything seemed fine, but some users (not all, but significant amount) expirienced troubles: when they trying to save a draft of message or create and send a message outside of organization, Outlook window with message became fozen fo a while (15-30 secounds). Inside mail not causing such thing. After that, message sending/saving normally. Somebody can help me with that? What can it be?