550-Verification failed for \n550 - Sender verify failed

I'm having problem deliverying mail to some hosts, and this is the logged error I see listed in Exim stats:

from remote mailer after RCPT TO:: host
xxxx.com [xx.xxx.181.73]: 550-Verification failed
for \n550
Sender verify failed

Any idea what to do to fix this, I have this happening on some machines with Cpanel and security fixes only...perphaps I'm missing something (i'm sure I am)

Thanks in advance

 

 

 

 

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