The various couriers supply us with 9 x 12 envelopes sometimes called Overnight Letters and large 12 x 18 envelopes called Courier Packs and other trade names.  Pricing of courier services are often linked to the size of the envelope.  The Mail center will make packaging selections for you since we stock all sizes and we will use the lowest-priced envelope for your mailing. 

Envelope Selection 

The size of the envelope should properly accommodate the size of the contents.

  • The size should properly accommodate the enclosure.  Excessively large envelopes will not keep the enclosure firm.  The enclosed items in such envelopes slide about and create an imbalance of the envelope, risking ripping, and loss of the contents.  A snug fit keeps the enclosure firm in the envelope for effective mail handling.
  • Conversely, when an envelope is overstuffed it can burst at the seams upon impact with other mail.  The result can be a total loss of the mailing.
  • The strength of the envelope should be such to withstand the weight of its contents.  If there is stress at the seams or sharp edges, then the envelope is overloaded and it can burst or rip and possibly lose its contents. 

For use in the U.S. Postal System, there are two categories of envelopes, Letter size, and Flats, as referred to by the U.S. Postal Service.  Letters and non-letters, or Flats, are rated differently by the USPS.  To assure the best rate, call the Mail center for sizes and rates before preparing the mail piece.

Letter Size

Letter-sized mail must be rectangular in shape for automated processing by the USPS.

To ensure prompt and efficient processing of First Class Mail it is recommended that all envelopes and cards:

(a) Have an aspect ratio of width (height) to length between 1 to 1.3 and 1 to 2.5 inclusive.  Contact the Mail center for an envelope template if you are not sure of sizing.

(b) Be sealed or secured on all four edges so that they can be handled by machines.

(c) The following dimensions must be met for automated processing by the USPS:

      Height- Min 3.5 " Max 6.125"
      Length- Min 5 " Max 11.5 "
      Thickness- Min 0.007 Max 0.1875"

Note: Maximum thickness for automated processing is 1/4."  Mail that does not meet the automated processing size may not qualify for discounted rates.

Flat Size

Flats are envelopes larger than the maximum letter size but not larger than 15" in length by 12" high (15" x 12").

International Letter Size Envelopes

Mail in letter-sized envelopes for delivery to foreign countries should be placed in "International" envelopes.  These envelopes have a red and blue border, which assures the proper posting of international postage rates and will prevent mailings from being returned for insufficient postage.

Red and Blue Bordered

Red and blue bordered envelopes are used only for Airmail to foreign countries.  These should not be used for mailings within the United States since there is no Airmail class for U.S. mail.

Plain White or Manila

Plain white or manila envelopes can be used for all other classes of mail.  These must be marked to show the proper class of mail; i.e. First Class or Parcel Post.


Padded envelopes contain a cushioned lining to provide a degree of safety for mailing small and fragile merchandise.  Padded envelopes are available from the Mail center on request.  We also stock computer disk mailing envelopes.


Priority envelopes should be used for First Class Mail weighing over 11 ounces and other mail under 11 ounces requiring expedited delivery.  Priority envelopes are red, white, blue, and available from the USPS free of charge.


Couriers supply us with mailing tubes for odd-sized long items as well as various other sizes of boxes, such as five pound boxes.  Our contract rates are linked to packaging, so the Mail center will select the right box for you.  We stock many sizes of boxes to provide you with an appropriate selection.

Contact Us

Physical Address
Mail Center
Carl Parker Building, room 109B
Lamar University

Mailing Address
Lamar University Mail Center
P.O. Box 10080
Beaumont, TX 77710-0080

Ph: (409) 880-2232
Ph: (409) 880-8485
Fx: (409) 880-2202

Have Suggestions or Comments?  Email PostOffice@Lamar.edu

Campus Map

Office Hours & Location

  • Office Hours
  • The Mail Center (Post Office) is located in the Carl Parker building, Room 109B
    (between the Setzer Student Center and the Mary and John Gray Library).