Mark Crispin writes:
“In particular, doing things with mailboxes in the hundreds of MB in that format takes a while. The authors of Outlook and Thunderbird are victims of a computer science course mindset which, starting in the 1980s, taught their pupils that all protocols are (or should be) stateless. Thus, they believe that IMAP is like HTTP; that when a server fails to respond immediately, that means that the correct remedial action is to disconnect and try again, or just disconnect and assume that everything happened anyway.”
Managing organized complexity 