Which mailpiece can be classified under the non-machinable letter price?

The classification of mailpieces under the non-machinable letter price refers to items that cannot be processed by automated sorting machines due to their size, weight, or contents. In this case, a 2 oz USPS Marketing Mail letter with an ink pen enclosed meets these criteria because the presence of the pen makes the letter rigid and uneven, which interferes with the automated processing equipment.

This means it cannot be sorted efficiently by machines designed for standard letters, thus necessitating manual handling. Non-machinable letters incur a higher postage rate due to the additional labor required for their processing.

In contrast, the other options do not fit the non-machinable criteria. First-Class Package Service is a distinct category used for parcels, not letters. Standard postcards are designed to meet specific dimensions that allow them to be machinable and processed easily. Lastly, Express Mail, while offering tracking options, is also designed for packages and not classified as a letter that could be deemed non-machinable.