A mortgage servicer is mortgage company that monthly payments get paid to. They may not technically own the home loan. Rather, they are the company that collects the payments and is the point of contact for the homeowner.
A mortgage servicer typically only communicates with the person on the note. For example, if a husband and wife own a home together and the loan was done soley in the husband’s name, the mortgage servicer won’t provide any details to the wife since she’s not on the loan. (We know, that’s messed up.)