On 29.01.21 09:41, Arjen Van Drie wrote: > ETRN ? That's an old SMTP command, used from nodes that are not continuously online.
Imagine two SMTP relays, A and B, where A is configured to forward some mails (e.g. for a domain) to B. But if B is not always online, e.g. because of a dial in connection, A would try to deliver to B, and if B is currently down, put it in the spool directory to deliver it later. So when B goes up, it would not immediately receive mails from A, since A waits for the next shedule to try again. In the worst case, B is down again when A attempts delivery again, and mail is never delivered. Therefore, there's the ETRN command, where B can notify A and tell „hey, i'm currently up, try it again” to trigger A to attempt delivery all mails for B immediately instead of waiting for the next schedule. This, however, still requires that A can open an SMTP connection to B. regards Hadmut
