Mikael Bak wrote: > Brian Evans - Postfix List wrote: > >> Mikael Bak wrote: >> >>> Santiago Romero wrote: >>> >>> >>>> Really, reject_unverified_recipient feature is very nice, but rejecting >>>> all mail when primary MX doesn't answers breaks it for us :( >>>> >>>> Any idea? :? >>>> >>>> >>> Hi, >>> >>> Quoting the documentation[1]: >>> >>> "The unverified_recipient_defer_code parameter (default 450) specifies >>> the numerical Postfix SMTP server reply code when a recipient address >>> probe fails with some temporary error. Some sites insist on changing >>> this into 250. NOTE: This change turns MX servers into backscatter >>> sources when the load is high." >>> >>> So you are not rejecting any email if the MX is down. You are just >>> delaying reject or accept until the MX is asked if there is such user or >>> not. We're very happy with this over here. >>> >>> >> No, you are not "delaying reject". >> You are bouncing and possibly BackSattering because you really don't >> know if the recipient is valid. >> >> Many, many envelope recipients are forged these days. >> So you end up bouncing to the wrong place and sending spam to a 3rd party. >> >> A good MTA in the world will hold a 450 for 3 to 5 days and keep retrying. >> If it doesn't retry, it's usually a bot and bad for your health. >> >> > > Hi Brian, > Well, thank you for sharing this with me. > > IMO this setup does not bounce as you say, it sends a "450 Address > verification in progress. Try later.". When the client tries next time > there is either an OK the address exists, or a 550 User does not exist. > > Maybe I don't understand what you try to say. I just don't see why this > would generate bounces or backscatter. > > Mikael > > I was referring to the "change to 250" that was quoted. I inferred that was the advice being given.
If this was incorrect, then, yes, it is just fine to use.
