For some of our clients who use MS365, we noticed that recipient verification _sometimes_ fails (actually, it fails more than it succeeds). What I mean by „fail“ (lightly edited for privacy reasons):
> > (EHLO and STARTTLS ...) > < 220 2.0.0 SMTP server ready > > EHLO (ourserver) > < 250 DB5EUR01FT011.mail.protection.outlook.com Hello [91.208.173.165] > > MAIL FROM: <support@(us)> > > RCPT TO: <(random non-existing email address)@(customer)> > > DATA > > [..] > > . > < 250 2.6.0 <[email protected]> > [InternalId=15603616188757, Hostname=DB7PR03MB3804.eurprd03.prod.outlook.com] > 9393 bytes in 0.135, 67.925 KB/sec Queued mail for delivery This obviously produces a bounce later on. By „succeed“, I would expect a 5xx response after the RCPT TO, which happens in maybe 1 in 10 cases, but we have not found a real pattern. According to docs, verification of RCPT TO should be enabled by setting the domain as „authoritative“ on MS365 (this setting has been confirmed). Delivery to existing accounts works as expected. Anybody else noticed this behaviour? — Matthias -- Matthias Leisi Katzenrütistrasse 68, 8153 Rümlang Mobile +41 79 377 04 43 [email protected] Skype matthias.leisi
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