Can I hire a process server to deliver a personal letter?

I need to send a formal “you are not to contact me in any way” letter to my ex, in a way that proves he personally received it. Because I do not want to share any actual address with him (not even my po box), I need to find a solution other than certified mail. A process server was suggested, but as I google, it looks like they’re for delivering court documents only? Are there any options like them but not only for court documents? Please note I can’t just get a restraining order; I’m looking specifically for help with sending this letter. Thanks.