USPS First-Class Flat service is a special cost-effective way to send non-time-sensitive items within First-Class Mail. Flats are large envelopes that are smaller than 11.5" x 15", and no thicker than 3/4" but larger than a regular envelope.

All large envelopes/flats must be rectangular or square-shaped and somewhat flexible. You can find out how USPS determines flexibility by referring to the USPS' guide.

Domestic First-Class Flat Service

• Pieces that exceed any of the maximum dimensions or are rigid, nonrectangular or not uniformly thick are charged the applicable First-Class Package Service price.

• A domestic First-Class Flat label is identified by a unique IMb barcode instead of a standard tracking number, so they cannot be tracked.

• Domestic First-Class Flat shipments cannot be included on a USPS SCAN Form or scheduled for a carrier pickup.

• Domestic First-Class Flat labels can be voided and refunded; voiding it before it is manifested (before 11:59 P.M. CT on the ship date) still returns a full refund.

For your mail to be considered a large envelope/flat, it must meet the guidelines below.

International First-Class Flat Service

• Pieces that exceed any of the maximum dimensions or are rigid, nonrectangular or not uniformly thick are charged the applicable First-Class Package International Service price.

• An International First-Class Flat label is identified by a unique IMb barcode instead of a standard tracking number, so they cannot be tracked.

• International First-Class Flat shipments cannot be included on a USPS SCAN Form or scheduled for a carrier pickup.

• International First-Class Flat labels cannot be voided or refunded once purchased, so confirm all shipment details before booking.

For your mail to be considered a large envelope/flat, it must meet the guidelines below.

If you are interested in using First-Class Flats services, please contact our customer service at 1.800.881.0288 or email servicedesk@descartes.com.

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