When SMTPDirect has a temporary delivery failure, it raises an exception with a list of the failed recipients. But OutgoingRunner leaves the message queued with the original recipient list. There's some logic in SMTPDirect to keep a list of undelivered recipients, but AFAICT only when an exception is raised by the lower-level delivery function, which doesn't happen for these temporary delivery failures. (The particular failure we see, pretty frequently, is a "450 -- enable to check MX record", for a single recipient, which results in almost the entire list getting the message over and over.)
Is this an oversight, or a design decision based on the behavior of the smtp delivery mechanism? If the former I'd be happy to fix it, but if it's the latter I'd rather not waste my time nor break our Mailman. :)
-les