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A comment on Maddy: Composable all-in-one mail server. Parent comment

Re:Maddy: Composable all-in-one mail server by upofadown on Saturday June 19, 2021 @08:22AM (#27559860)
That's odd. I know that Spamassassin actually penalizes HTML and HTML only email.

Are you sure there is not some sort of parasitic Bayes filtering happening here?

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Re:Maddy: Composable all-in-one mail server by g_p on Saturday June 19, 2021 @09:09AM (#27560158)
It's very odd. I don't know how Microsoft implements their own server-side spam filtering, but the issue was coming from their filters. No issues with any other host. G Suite accounts received plaintext mail fine.

I never found much by way of technical detail on 365 deliverability, beyond the usual DKIM/SPF/DMARC/PTR record guidance, and forms for getting yourself removed from the whitelist.

What's especially strange is that this issue applied even when sending mail as a 365 subscriber. Once there was HTML content present in the email, deliverability (to other separate 365 tenants) improved!

Very odd...

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