On Feb 20, 2025, at 12:13 PM, Rob McEwen via mailop <mailop@mailop.org> wrote: > > Starting earlier today (Feb-20-2025) AT&T/Prodogy/Yahoo started rejection my > users' emails due to my sending-IP-address (204.9.77.40) allegedly not having > rDNS, except it does
This is a long-standing intermittent problem; for example, see this mailop post from July 2021: https://list.mailop.org/private/mailop/2021-July/019617.html I see a background level of it always happening at a low rate (although much more today, as you say). If you use postfix, that message explains how you can mitigate this problem by adding this to an smtp_reply_filter: /^550 \d.\d.\d (Connections not accepted from servers without a valid sender domain.*)/ 450 4.7.1 $1 -- Robert L Mathews
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