Winthrop University: Post Office - Mailing - Types of Mail
Contact Information
Post Office
DiGiorgio Campus Center
Rock Hill, SC 29733, USA

Post Office

Types of Mail

Knowing the shape of your mail helps select the right services.

Large Envelope

  • Large envelopes are flat, rectangular mail pieces, no thicker than .75 inches.
  • The contents of these envelopes must not contain anything that cannot be bent. If the contents are not flexible, the envelope must then be charged to a parcel rate.
  • The minimum size is 11.5 inches in length and 6 1/8 inches in height. Any envelopes under this minimum, but over letter minimum, will be sent First Class letter rate.


  • Small rectangular mail pieces no thicker than .75 inches.
  • The maximum size for a letter is 11.5 inches in length and 6 1/8 inches in height. Any piece exceeding this size will be sent as a flat, unless it's contents contain something that cannot be bent. If the contents contain something that cannot be bent, the letter will then be classified as a parcel and receive parcel rates.
  • The minimum size for a letter is 5 inches in length and 3.5 inches in height. Letters not meeting the minimum size cannot be mailed.


  • Any item over 25 pounds must be brought to the Post Office in the lower level of the DiGiorgio Campus Center, as postal personnel are unable to accept items over 25 pounds. The Postal Specialist must walk for most of their route so they are unable to pick up any articles or mailings with a single piece weight of over 25 pounds.
  • A three dimensional mail piece contained in a box, thick envelope, or tube weighing up to 70 pounds. Length and girth (distance around the thickest part of the package) cannot exceed 130 inches.
  • Large mailings can only be picked up in USPS mail buckets or trays. Please contact us in advance if you need buckets or trays delivered to you.
  • We will pick up as many mailing tubs as you need as long as the individual weight does not exceed 25 pounds. We ask that you call the Post Office at 803/323-2293 if you have a heavy mailing going out so we can plan our pick-ups accordingly.


  • A postcard is a rectangular cardstock mail piece not contained in an envelope.
  • The maximum size for a postcard is 6 inches in length and 4.25 inches in height. Anything over this size is considered a letter and must have first class letter postage.
  • The minimum size for a postcard is 5 inches in length and 3.5 inches in height. Anything under this minimum size cannot be mailed and is not considered by the Post Office as a qualified piece of mail.
  • When creating a post card, be sure to put the mailing address to the right side, towards the bottom, leaving room on the right side top for postage.

Last Updated: 7/13/22