First Class Letters & Flats
Teapplix does support printing First Class Letters & Flats. There are some special considerations when printing these type of labels.
1) Package Identification Number
First Class Letters & Flats do not have real tracking numbers. Instead they return a "Package Identification Number". This number can not be tracked on USPS site. However, you can obtain some limited scan event information from Endicia web site using this URL:
For Stamps.com, the Package Identification Number cannot be tracked on USPS site nor Stamps.com site..
2) Physical Requirements
Typically, USPS requires merchandise to be shipped using First Class Package, and may reject your mail send in using First Class Letter, or First Class Flat. The "physical requirement" include that your mail piece have uniform thickness, and be able to "bend". The best source of this information is from the USPS site: pe.usps.com, find the "Quick Service Guides", the current link is provided below but subject to change on USPS:
3) Confirmation to Customers
When you ship an order using USPS First Class Letter or Flat, Teapplix will mark your order shipped on the marketplaces, but will not provide a tracking number. This is to avoid the confusion to the buyers. Also some marketplaces such as Amazon have restricted requirement that all number set as tracking number must by trackable.