Can I use a Certificate of Mailing for filing a new patent application?

No, you cannot use a Certificate of Mailing or Transmission for filing a new patent application to establish the application’s filing date. The MPEP explicitly states:

No benefit will be given to a Certificate of Mailing or Certificate of Facsimile Transmission relative to the filing of a national patent application specification and drawing or other correspondence for the purpose of obtaining an application filing date.

This restriction is also specified in 37 CFR 1.8(a)(2)(i)(A), which excludes “[t]he filing of a national patent application specification and drawing or other correspondence for the purpose of obtaining an application filing date” from the Certificate of Mailing or Transmission procedure.

However, it’s worth noting that new patent applications can be filed electronically via the USPTO’s Electronic Filing System (EFS-Web), which provides its own timestamp for filing date purposes.