Since Dan asked about this, I thought I’d post an update about how I’ve changed my mail-reading habits.
Previously, I was using Gnus for all my mail-reading. Mostly, this worked well. However, some poor implementation decisions (which is the only way I can understand what was happening) in Gnus’ IMAP support meant that moving emails between folders or deleting emails from folders was an extremely slow, tiresome process. Additionally, Gnus doesn’t background the process, so moving an email to the spam folder (so the server-side spamassassin would pick it up) or deleting an email made Emacs unusable for several seconds.
It turns out that, for me, this is only a problem with my INBOX. Mailing lists are sorted server-side (using Mail::ListDetector) and the only time I really need to move something is when spam hits my inbox. That or deleting some automated messages from my server.
The solution was easy: start using Mozilla’s Thunderbird for the INBOX and continue using Gnus for everything else. This way I can quickly deal with the spam and server messages and continue reading the other email and newsgroups in the environment that I’m most comfortable.