On Thu, Aug 27, 2009 at 10:57:32AM -0700, Ben Dunlap wrote: > > another change in the email admin best practices discussion. For a short > > while the network became clogged in bounce messages sent to both valid > > and invalid addresses. Some of the invalid addresses even triggered > > infinite loops of error messages. None of the servers I am familiar with > > send bounce messages reporting invalid addresses any more. Our own > > servers won't even tell us internally when they discard incoming > > messages. SPAM quarantine is a thing of the past. > > Seems like there's another possible way to handle messages to invalid > addresses, though; the receiving SMTP server can simply reject the > "RCPT TO" command with a 5xx error. This avoids backscatter but also > lets well-behaved clients know that the destination address is > invalid. AFAIK this is how Rackspace Email works (if you don't have a > catch-all address configured).
There are two issues with this. First, when a service like Yahoo, with millions of customers, has an SMTP conversation, it would have to check for each RCPT TO address while the conversation is going on. I can imagine they would consider this a problem. It's simpler for them to simply accept the mail and issue a bounce later when they've done their checking (which is what a lot of them currently do). The second problem is that it still forces the originating SMTP server to pass on the 5xx error as a bounce message to the originator. The fact is that, according to what I know of the RFCs, SMTP servers are supposed to reject bad addresses with a 5xx error during the SMTP conversation, as you describe. But it appears that a lot of servers don't follow the RFCs. Paul -- Paul M. Foster -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
