I would be happy to help you with this. An E-file is an electronic file, basically the forms are sent 9in a format similar to PDF files over the internet. Filing by mail is printing the forms out and sending them through a postal service. I would personally recommend using the US postal service, but I'm sure you could use fed ex or UPS or another postal service.
Here is information on how to file by mail.
You can find out here https://www.irs.gov/uac/where-to-file-paper-tax-returns-with-or-without-a-payment