Well my email server doesn't trust their email server...
Mar 21 14:15:18 **** postfix/smtpd[4727]: NOQUEUE: reject: RCPT from 50-200-96-175-static.hfc.comcastbusiness.net[50.200.96.175]: 450 4.7.1 <e2016b.eqpnet.lan>: Helo command rejected: Host not found; from=<****@equipnet.com> to=<*******> proto=ESMTP helo=<e2016b.eqpnet.lan>
... and sadly their email server doesn't trust my email server since somehow PlusNet put my IP range back into the SpamHaus PBL but that is resolved now after appealing last night.
Mar 22 20:04:08 **** postfix/smtp[28365]: B5D12161737: to=<*****@equipnet.com>, relay=mail.equipnet.com[50.200.96.179]:25, delay=3.9, delays=0.02/0.07/1.2/2.6, dsn=5.0.0, status=bounced (host mail.equipnet.com[50.200.96.179] said: 554 Service unavailable; Client host [****.plus.com] blocked by zen.spamhaus.org;
https://www.spamhaus.org/query/ip/**.**.**.** (in reply to RCPT TO command))
I could add e2016b.eqpnet.lan as a trusted name... but I'm not sure I should since really it is their side that is misconfigured.
That old nagging doubt says.... don't touch with a barge pole.