Mailing in's and out's
There are several choices when it comes to sending in paperwork to the PTO. Certain methods of mailing are not allowed for specific types of correspondence. There's "Priority Mail Express", Certificates of mailing, the EFS (electronic filing system), and Certificates of transmission. Never expect anything to be plain and simple when it comes to the PTO.

A Certificate of Mailing is a piece of paper stating the date that the listed documents were mailed. When using a Certificate of Mailing, the filing date is always the date the correspondence was sent, never the date it was received. These Certificates are basically a promise sheet that list out the documents that were sent along with the date they were sent.

"Priority Mail Express" can be used for sending in any type of document and any type of application. It is a reliable and easy method of mailing through the United States Postal Service (USPS). The filing date is the date on a correctly labeled "Priority Mail Express" mailing label filed with the USPS. No Certificate of Mailing is required when this method is used.

Faxing may be acceptable for some forms sent to the PTO. When faxing anything to the PTO, a Certificate of Transmission should be sent along with the document that is being faxed. A Certificate of Transmission is a paper stating the date and time the listed document was faxed to the PTO.

The filing date for a document sent with a Certificate of Transmission is based on the time stated on the Certificate of Transmission, as opposed to the time it was received by the PTO. This mode of transmission may not be used for many different documents, like paperwork requiring an original signature or papers that will obtain an application filing date (and the list goes on and on).