Our e-mails are more or less mission-critical, so we try to send, then try to send again -- I suspect the additional failures are causing this to back up a bit. For concrete numbers, of 27 e-mails we tried to send, only 2 got out successfully.

Also of interest is that I only got a 454 ("Temporary service failure") three times -- the rest of the time, it just freezes/times out in ssl.