"sender's mail server is blocked"

[thingwarbler]

A client of mine complains that he's seeing bounces from an email recipient. I've checked blacklists, and my mail server's IP does not show up. The bounceback says:

Reason: Remote host said: 554 5.7.1 <mail.xxx.com[xx.yyy.zzz.www]>: Client host rejected: The sender's mail server is blocked

-- The header and top 20 lines of the message follows --

Received: from static-64-222-187-6.man.east.verizon.net

What does this mean? Is it just the recipient's ISP that's loopy? I don't think it's an SPF issue -- that would have given a greylist response anyway, right?

Mail server is on a dedicated IP on a VPS server.

 

[tanmaya]

SPF and greylist are not related.
Doesn't looks like a mail loop or an SPF issue.
It will be better to contact mail admin of recipient mail server and ask them about the possible cause.