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Outgoing Mail

This is valuable information for students, staff, and faculty who send their mail through Rensselaer Mail Services. These are the guidelines established by the USPS (United States Postal Services) for addressing mail. These guidelines should be observed for all mail, including campus mail.


The size of an envelope should properly accommodate its contents. There are basically two categories of envelopes used by the USPS: letter size and flats.

Letter Size

Letter size mail must be rectangular for automated processing by the USPS. To ensure prompt and efficient processing of First Class mail, observe the following guidelines:

  • All envelopes and cards must be sealed or secured on all four edges so the machines can handle them.
  • The height of the envelope must be at least 3 1/2" and no more than 6".
  • The length of the envelope must be at least 5" and no more than 10 1/2".


Large mail pieces must be sorted without bending so they remain flat. Flat-size mail exceeds at least one of the letter size maximums, but is restricted to the following dimensions:

  • Length: 5" to 11 1/2"
  • Height: 6 1/8" to 12"
  • Thickness: 1/4" to 3/4"
  • Weight: no more than 16 ounces

A flat may be unwrapped, wrapped, or enclosed in an envelope. Read more

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