First-Class Flats 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.

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Domestic First-Class Flat Service

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

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. Large Envelopes/Flats shipped via First-Class are not able to be tracked, voided or refunded.

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. Large Envelopes/Flats shipped via International First-Class are not eligible for tracking but can be voided.

If you are interested in using First-Class Flats Services, please contact our customer service at 1.800.881.0288 or email info@xpsship.com.

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