I've tried following the instructions here and here. Currently, I can read email from my GMail account, but not send—this is on a personal computer, so even if I configured Sendmail, I doubt any of the mail would survive the spam filter gauntlet. Both guides seem to require the --enable-smtp option for mutt, which I don't think is being exposed by ports. I've tried the mutt and mutt-devel ports and neither seem to give me that option.
On a far less important note, I also haven't been able to change folders, e.g., I get told that Sent Mail is not a valid folder when I attempt to go into it. If you can troubleshoot this problem, it's pure gravy. I really only care about sending.
Thanks,
Hank
UPDATE: For those who are interested, the mutt wiki has a GMailOverIMAP UserStory.
UPDATE 2: Although I finally solved my original problem (enabling SMTP support for mutt in FreeBSD), @grawity convinced me to use a relay and avoid mutt's native SMTP support. With that in mind, I went with msmtp. At that point, The Quick-N-Dirty Guide to Using mutt with gmail was very useful, including tips on how to enable OpenSSL for msmtp (so it can talk to GMail's SMTP servers, which use TLS).