We run an e-mail server for a few customers, and we've recently run into a bit of a conundrum.
We had a user who sent an e-mail to an incorrect e-mail address. The incorrectly specified domain unfortunately existed. It did not have MX records, and the A record of the domain went to a server which did not speak SMTP. Therefore, the e-mail server attempted delivery and did not succeed because no e-mail server was running.
For that reason, our e-mail server, entirely in accordance with the SMTP RFC, attempted re-delivery over the course of five days and finally gave up and sent a notice to the sender after 5 days of unsuccessful delivery.
Section 22.214.171.124 of RFC5321 (Simple Mail Transfer Protocol) says:
Retries continue until the message is transmitted or the sender gives up; the give-up time generally needs to be at least 4-5 days.
Therefore, the mail server in its default configuration, in this case has operated in accordance with the RFC, meaning that a user specifying the wrong e-mail address in this case would not receive notice of that except five days later.
At this point, my boss has asked whether it would be possible to reduce the give-up time to something shorter, say 1 day. His reasoning is that it is better that the user be notified earlier of non-delivery, and that the user may attempt re-delivery at a later date, or delivery through an alternate channel. It sounds like a reasonable thing to do, but in general I'm wary of performing any kind of configuration changes which contradict what's in the RFC.
Is there any non-obvious reason why it would be a bad idea to reduce the give-up time to 24 hours, beyond just saying "the RFC says otherwise"?
Also, what do the bigger e-mail providers out there (the Googles, Microsofts, AOLs and Yahoos) do in this scenario?
sendmail, for example, also sends a warning that delivery has not yet been successful, at (I think) the four hour mark. Since those also say who it's from and to, the user should get warning that something's up well before the five-day failure mark. If your MTA doesn't generate those warnings, then choice of MTA probably is a factor.