On 12 May 2018, at 17:55 (-0400), Thomas Smith wrote:
The documentation[1] and several e-mails here mention that
reject_unknown_client_hostname can reject legitimate e-mails.
What exactly are these scenarios? When do they occur in real life? Are
there really legitimate mail servers that don't have a reverse DNS
record that resolves to their IP?
Yes. Examples:
1. One of the outbound mail servers for my state government (Michigan,
USA) has 5 PTR records, 2 of which give names that don't resolve. So,
40% of the time it would hit reject_unknown_client_hostname.
2. Occasionally, DNS for some of the outbound mail servers for Office365
goes bad and the reverse names for a subset of them return NXDOMAIN
temporarily.
--
Bill Cole
b...@scconsult.com or billc...@apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Currently Seeking Steady Work: https://linkedin.com/in/billcole
