Re: [client] did not issue MAIL/EXPN/VRFY/ETRN during connection

Claus Aßmann wrote:

Maybe you should try to connect from some "remote server"s
to yours and see what happens?
That is, can you reproduce this weird reply?
If so, then it's not sendmail that's replying...

I cannot, unfortunately, use Proofpoint servers. I have to trust what they are notifying the sender as what's going on - and the above was the only note aside of the original message/headers, that tells me something, albeit in a very cryptic way.

If you can't reproduce this, maybe you should post the name/IP
of your MTA so others could help?

No problems in sharing, but it is puzzling I get over 100k emails/day from all kinds of providers but not from a handful of large enterprise names. I was leaning towards not being a problem on my end, as your responses makes me feel like, but wanted to try harder before I approach these folks and ask them to work with PP. About Cisco, that's a different animal altogether and I have no idea yet.

Try_TLS:                                YES,VERIFY,ENCR
TLS_Srv:                                VERIFY,ENCR
TLS_Clt:                                VERIFY,ENCR

How did you come up with these entries? That is, which part
of the documentation says these entries are correct?

Those I have to look on our archives why and when were added (been there since first versions I could find, dated from 2016). But again, judging by your question, I'm almost positive those are not correct.
I appreciate your time and directions. All things considered, if after all your highlighted points are removed things still look bad, I shan't blame my infra - for now.