I'm using Mercury/32, v4.90.298 with SMTP Client (end-to-end version).
In the past three days, I've seen six emails being sent to known valid addresses that fail with:
Permanent error 250 (no data or no address - name server conf) resolving 'validdomain.com'
Checking the MX records for the domains finds all of the failures are pointing to something like validdomain-com.mail.protection.outlook.com
In each case, after the failure, checking the DNS records shows no DNS problems, and resending the message succeeds.
I searched logs back a few months. It happened twice in December. None in January. Four times in February. Three times yesterday, and once so far today. (Edit: twice today now.)
They are apparently transient errors, but the error message indicates permanent failure.
Anybody else seeing anything like this?