I can't tell if people truly believe response codes and enhanced codes are used uniformly and reliably out in the wild, or if they are just talking about their own personal systems and the codes they throw. Setting any kind of hard rule based on 5xx/4xxx or x.x.x is completely irresponsible if you're sending email at scale for tens of thousands of distinct senders. When I was actually doing this kind of thing for a living, you could give me any response/enhanced code combination and tell me what I was supposed to do with it (retry, don't retry, permanently suppress) and I could give you 100,000 messages sent in any given week that would disprove the rule.
At one point we had a hard rule to suppress addresses returning 550 5.?.?. I can't remember the code. One day Hotmail has a bug and starts throwing millions and millions of these responses at us. We ended up adding *hundreds of millions* of good addresses to our users' suppression lists because *clearly* this was a hard bounce and they were invalid addresses. The code says so. As a sender, the only way to keep up with the insane responses (both codes and strings) that come back from remote servers is to have someone who manually review response handling rules daily or weekly. What is also helpful is crowdsourcing improperly handled responses from your users who care enough to review their SMTP logs; "hey looks like this should be a retry, not a bounce." After a while you'll end up with a system that is pretty good at doing the right thing in most circumstances. Luke On Thu, Sep 19, 2019 at 9:14 PM Jay Hennigan via mailop <mailop@mailop.org> wrote: > On 9/19/19 20:38, Lyndon Nerenberg via mailop wrote: > > > Others have hinted at this, but let me call it out explicitly: > > > > Pay attention to the SMTP Enhanced Status Codes > > > > A [45]XX can be graduated by the associated [45].X.X. > > Add to the below list, if you get a 550 5.7.1 you need to stop mailing > and look very hard at your customer's list gathering practices. Either > the receiving system's sysadmins or the individual recipient is > intentionally refusing mail from you specifically. > > > E.g.: > > > > 552 5.2.3 > > 552 5.3.4 You sent something too porky for the recipient. That's > > *your* fault, not theirs. > > > > 452 4.3.1 The entire destination system is out of disk space. > > Likely not the recipient's fault. > > > > 5XX 5.3.5 The sysadmins running the recipient's mail system are > > not top notch. Not the recipient's fault. > > > > 550 5.6.9 The recipient is hosted on a server running old software > > that fails on UTF8 headers. While they might lose > > some of the messages you send their way, this isn't > > necessarily an excuse to boot them from the list > > outright (unless the majority of your traffic > > provokes this failure). > > -- > Jay Hennigan - j...@west.net > Network Engineering - CCIE #7880 > 503 897-8550 - WB6RDV > > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop >
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