Can you confirm whether RBL has blocked, or some other third party spam blockers ?
Can you post the exim error log here in order to check ? Normally there might be some spamming issues in the server (Out going spam) which makes the server's ip to be blacklisted.
On identifying the spam origin, request your customer to check with the exim configuration and server security. If you require more help on this, let me know.
Bounce message:
XXX.XX.XX.XX does not like recipient.
Remote host said: 550-"JunkMail rejected - oproxy14-pub.mail.unifiedlayer.com
550-[67.222.51.224]:49314 is in an RBL, see Currently Sending Spam See:
550 http://www.sorbs.net/lookup.shtml?67.222.51.224"
Looks to me, to be just what I said, the customer's email server is/was temporarily blacklisted.
Please remember, this is an email bounce from a customer email coming TO me, on one of my
cpanel servers. My server is rejecting it, just like it's configured to do.
Last week it was a different host address, but from the same email address.
The IP's are not even in a single class-c, which is why I would like to whitelist
the email address, or email domain, and cannot just whitelist the IP.
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If you have Mailscanner installed you can do this in Mailscanner>>>>MailScanner Front-End>>>>Server Spam Whitelist
I have installed mailscanner from ConfigServer, and I don't see any such configuration available in WHM, just the rules files to manually modify.