On 3/5/10 7:08 AM, David E. Smith wrote:
As long as we're going off-topic, might as well go all the way :V
How long should a sender (say, Facebook) retain a database of 5xx SMTP responses? Just because jimbob@school.edu doesn't exist today, doesn't mean that James Robert Jones won't enroll in the fall and get jimbob@ as his school-provided email address.
They really don't need to retain it at all, other than perhaps to count a few messages to determine to remove the address. A 5xx response is a permanent failure. "The specific message you are sending to this address *right now* will never be delivered, don't keep trying to send this specific message." This usually means that the address does not exist, is administratively prohibited from receiving messages, the MTA is blocking the sender, etc. It is possible but unlikely that a future message from the same sender to the same recipient will succeed. Some mail systems with "dirty word" filters may return 5xx to a specific message and allow another with different content. These aren't all that common. Things like a user going over quota or a temporary failure should not return 5xx but 4xx. Facebook (and legitimate senders of periodic subscription emails) should remove that address from their subscriber lists after receiving 5xx responses. Some subscription services will delete an address only after a series of 5XX rejects (three in a row for example) rather than just one to guard against a fluke erroneous response. If in the future jimbob@ gets assigned that address and chooses to subscribe, then it can be re-added. -- Jay Hennigan - CCIE #7880 - Network Engineering - jay@impulse.net Impulse Internet Service - http://www.impulse.net/ Your local telephone and internet company - 805 884-6323 - WB6RDV