First, there are no mail deliveries in Mongolia. All mail is sent to a post office. You have to include the recipient's phone number because the Mongolian post office will phone the recipient to advise he/she has mail...and they will charge a small fee when the mail is picked up.
FedEx and UPS do not ship to post office addresses. I think FedEx provides some service to Mongolia via another airline. Not sure where the connection is. And, the shipment will go only to the capital, Ulaanbataar.
I ship frequently to Mongolia. My daughter lives there. I send the shipments to BidMongol Express in California. They forward shipments onward either via air or ocean. You have to tell them which you want. Air, of course, is much more expensive. You do not pay BidMongol. The recipient in Mongolia pays the transportation fee. Shipments go to Ulaanbataar, but they will forward to final destnation, usually by taxi. Thus far we have sent many shipments with 100% reliability. If you want more info about them, contact their manager, Ogi Erdenebat. Email ogi@bidmongol.com.