Granted, I'm using an old-ish version (1.4.2.2i) but I'll report this just in case newer releases are still misbehaving.
In short, Mutt sent my email and then chucked it into bit-heaven because I had specified an invalid Fcc. That's bad! Very bad!! A nicer behaviour would have been backing up my message to a dotfile in my $HOME (like Slrn does). BTW, the invalid Fcc I had specified was '.' (what I was trying to say was "put it in the friggin' current mailbox!" - there *should* be a quick way to say this, in case there still isn't). -- ~> cat /etc/redhat-release && uname -a Scientific Linux SL release 5.1 (Boron) Linux acerrimo.local 2.6.18-92.1.6.el5 #1 SMP Wed Jun 25 12:46:39 EDT 2008 i686 athlon i386 GNU/Linux