For reference, a couple of samples of the blocked emails are: NOQUEUE: reject: RCPT from o4.email.wetransfer.com[192.254.123.89]: 554 5.7.1 Service unavailable; Client host [192.254.123.89] blocked using zen.spamhaus.org; from=<bounces+922094-4e0b-(redacted)@em9713.email.wetransfer.com> to=<(redacted)> proto=ESMTP helo=<o4.email.wetransfer.com>
Zen list is an amalgam of XBL, PBL, SBL, SBLCSS & PBL blocklists Data can be transient or delisted ... policy depends on the specific list. What were the return codes for the rejections above -- at the time of rejection? When did you *check* listings, relative to the rejection time stamps? What is your 'postscreen_dnsbl_threshold' setting, and wow are you scoring the individual spamhaus return-code ranges?
