Each student requesting a letter will email you a form from Interfolio. It will describe two methods for submitting your letter: through the internet or through the mail.
The internet method involves two steps. First, open a writer's account with Interfolio; doing so is extremely easy. Second, electronically transfer your letter using Interfolio's website.
The letter will be stored as a PDF file on Interfolio's computers. Interfolio will accept and convert electronic files in the following formats: .pdf, .doc, .docx, .rtf.
You can add a signature to your letter by faxing it to Interfolio. Or, if you want to take the trouble, you can scan your signature and insert a picture of it into the electronic copy of your letter: you will need to be handy with a scanner, the relevant software, and templates for your word processing documents. If your letter will not have any signature at all, you might want to add a line explaining the reason why.
Letters sent to Interfolio through the regular mail are scanned (much like a fax machine does) and stored as electronic images on Interfolio's computers.
For speed and quality, the internet method is preferred, but the regular mail works fine.
Faxing a letter to Interfolio produces very poor results and should be avoided if at all possible. If you have run up against the deadline and are unwilling to establish an account on Interfolio on your own, the department administrators can help you open an account (it must be in your name) and upload your letter.