On 9/29/2014 9:28 AM, Wietse Venema wrote: > Noel Jones: >>> By default, Postfix sends address verification probe messages via the >>> same route as regular mail, >> >> Yes, but it also says: >> >> Probe messages are like normal mail, except that they are never >> delivered, deferred or bounced >> - and - >> Postfix assumes that an address is undeliverable when the nearest >> MTA for the address rejects the probe, regardless of the reason for >> rejection > > This text needs to be updated. The old Postfix SMTP client behaved > as if smtp_mx_session_limit=1, that is, there was only one SMTP > session per delivery request (it tried to connect to each MX until > one responded, and then it would not try any of the other MXes). > > Why is it better to skip the fallback relay and reply with "4XX"? > > Wietse >
My impression is a typical smtp_fallback_relay would not validate recipients, therefore unable to give a meaningful answer. Conversely, if the fallback is an alternate path to internal storage it may have all the answers. Postfix currently has a method to turn off smtp_fallback_relay for verification probes (by using a separate transport) but it's not clear this is necessary. If the fallback is *not* used by design, there wouldn't be any way to turn it on in case it was desired. I know we can't document everything postfix *doesn't* do, but I think this needs clarification. -- Noel Jones
