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Business Mail 101 - Mail Characteristics
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Size and Shape

The Postal Service separates all mail into one of four size categories:

postcards
letters
large envelopes - known as "flats"
parcels

There are different prices and different standards for preparing your mail depending on the size of the mailpieces. If you have any questions about the size or shape of your mailpiece, contact your mailpiece design analyst (MDA) or business mail entry unit for advice.


Minimum and maximum sizes

Mailpiece shape