This sender is rejecting our sender verification attempts due to timeouts:
Jun 11 10:42:04 mx10 postfix/smtpd[15520]: NOQUEUE: reject: RCPT from gourmet.spamgourmet.com[216.75.35.164]: 450 4.1.7 : Sender address rejected: unverified address: conversation with gourmet.spamgourmet.com[216.75.35.164] timed out while receiving the initial server greeting; from= to= proto=ESMTP helo=
As a result we can't verify the sending MTA actually accepts mail at the purported sender address and the messages are rejected.
And furthermore:
The issue at spamgourmet isn't exactly that they don't verify senders but that connections to their servers take too long and time out prior to our verification attempt. It's possible this wasn't always the case: for instance, if they previously responded more promptly it's possible sender verifications were going through.
We may be able to whitelist this domain but it ultimately depends on the volume of mail receive from them and the potential for abuse. Is the address you need to receive mail from unique or are there multiple spamgourmet addresses?
Now I do not entirely understand this. I don't know if this policy of my ISP makes sense (other email places like gmail seem to receive from spamgourmet without problems). But is it possible for spamgourmet's servers to verify better / not time out / whatever? Would this make sense to do, given that possibly other ISPs may have the same policies, or might in the future?
Or, if this is not possible, what do you suggest I tell my ISP?
Thank you.