I suspect your webmail system is putting certain headers in the email, that Hotmail/Outlook detects, and Hotmail/Outlook have detected a issue with the particular webmail system, like a security issue that allows unauthorized users to send spam through the webmail system, causing Hotmail/Outlook to blanket block that particular webmail software.
My suggestion: Send an email to yourself from the webmail system, and then from a desktop client. Compare the headers. Then set up your outgoing SMTP server, to dump/modify those headers that the webmail system is putting in, effectively hiding that the mails are sent by that particular webmail software. NOTE: ONLY do this after you are sure that there is no issues with your installation of webmail software (ero either upgraded to latest version, or any security holes back-ported and patched). Else you risk either getting blocked, or causing other issues like Thunderbird becoming spam filtered (however pretty low risk of that). Från: Rob McEwen via mailop <mailop@mailop.org> Skickat: den 1 juni 2022 23:26 Till: mailop <mailop@mailop.org> Ämne: [mailop] outlook/hotmail (silently!) putting legit msgs into "Junk Email" folder RE: outlook/hotmail (silently!) putting legit msgs into "Junk Email" folder All of a sudden - my users are having either all or most of their webmail-sent legit hand-typed messages going to outlook/hotmail - placed into outlook/hotmail's "Junk Email" folder - specifically, when logged into the outlook/hotmail webmail site. But if the same message is instead sent by the user from their Outlook Desktop app or Thunderbird, it works. Fwiw, the accounts I tested had SFP and DMARK setup and working correctly. (fwiw, I'm using the same webmail setup that I've used for a long time - no recent changes there.) I've reached out to some of my contacts at Microsoft - so I'm waiting to hear back from them - but in the meantime - is anyone else seeing this? Any suggestions? The kind of messages getting blocked - would be the kind that I would be embarrassed by if my system were blocking such hand-typed not-spam business emails - this must be overzealous spam filtering - but if, in the meantime, I could find a workaround to get past this, that would be great! Also, I think this is appropriate for Mail Op because (1) others could be having this issue too, but not even be aware of this yet? These message are getting "250 OK" responses, so this won't get noticed as quickly! and (2) messages going to outlook/hotmail are a statistically significant percentage of all email, so this might be a new issue impacting many many people. -- Rob McEwen, invaluement
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