Since I found Tim's description useful (though I haven't had the problem myself), I'll add one: The recipient SMTP server closes the connecton before sending a final acknowledgement of having received it. The delivering server can't mark it as delivered, so re-queues it, and the process continues. Strangely, I've seen 2 addresses at the same domain with one exhibiting the above behavior and one not. Omar On Fri, May 04, 2001 at 05:43:06PM -0400, Tim Pierce wrote: > > We occasionally get a complaint that someone has received dozens > or even hundreds of copies of a single mailing list message. > Each time we've been able to track down the source of the problem, [...] > The gateway opens an SMTP connection with the internal POP server > and announces it has mail for 50 users. Suppose one of those users > has a full mailbox. The POP server will return a 450 response for > that user, meaning "can't deliver now, but try again later." > > The gateway *should* recognize that it should only try redelivering > to that particular user. Not all systems do recognize this. Instead, > they forge ahead and deliver the mail to the other 49 recipients, and > then turn around and re-queue it for all 50. In a few minutes it > redelivers the message to all 50, except for the one whose mailbox is > full. So it re-queues the message again. And so on.
