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