How does the messenger check the phone number?

1. First, check the fax header information. When receiving a fax, the fax machine will automatically print the fax header information, including the sender's name, address, telephone number and other information.

2. Secondly, check the contents of the fax file to open the fax file and check the contents of the file to determine the contact information of the caller.

3. Finally, inquire through the phone book, and get the contact information through the phone book or Internet search.