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.
