User email relaying and IP addresses

I am confused about what to put in the relay file for users who have a mail account with another ISP but use our domain email address as well. For example, our mail log shows a users login something like this:

Login user=fred host=host12-245-67-89.range12-245.domian.com[12.245.67.89]

Would I put 12.245.67.89 as his IP in the relay file, or the range? And would that be 12.245 or 12-245.

Thanks

Bob

 

 

 

 

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