The RFC language determines what the software must do in order to be RFC compliant. Violate a MAY or SHOULD and you're still compliant. Violate a MUST and you're not compliant. But nothing forces you to be compliant, although peer pressure might encourage it.
Sending response codes 450 and 550, including 550 5.7.1, for policy reasons is RFC compliant. As you noted, it's the rare MUA and MSA that doesn't add them, so, yes, rheir servers, their rules. Similarly for checking DKIM or SPF; it is perfectly RFC compliant to reject mail that doesn't contain them or doesn't pass validation. One more potential issue is that it is RFC compliant to reject mail from domains or IP addresses that you consider problematical. The better the reutation of your provider, the more likely that your mail will get through. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List [IBM-MAIN@LISTSERV.UA.EDU] on behalf of Grant Taylor [0000023065957af1-dmarc-requ...@listserv.ua.edu] Sent: Monday, December 12, 2022 7:19 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Why email from z/OS SMTP rejected by Gmail? On 12/12/22 4:49 AM, Seymour J Metz wrote: > That's a SHOULD, not a MUST. I don't recall whether the SMTP external > writer (z"l) generated message-id or whether the application needed > to include it in its sysout. You're using RFC language. Remember, each and every email operator is free to do what they want to. Google / Gmail has recently (~3 months?) been requiring headers to exist that almost all legitimate email has that spam is more likely to not have. Requiring a header to exist that all contemporary mail clients (MUAs) have added for more than 20 years, is a fairly safe thing. It's only atypical email sending systems, which aren't MUAs, that have been running into this problem. Or really old / unmaintained MUAs, likely from 20+ years ago. -- Grant. . . . unix || die ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
