321Certified generates labels, not envelopes
You'll need to purchase envelopes separately. Print your 321Certified label and affix it to your envelope before mailing.
4.125" x 9.5"
Best for:
Standard documents, letters, single-page legal notices
Capacity:
4-6 pages
6" x 9"
Best for:
Multi-page documents, small booklets, photos
Capacity:
10-15 pages
9" x 12"
Best for:
Full-size documents, legal filings, thick packets
Capacity:
25-30 pages
Follow these guidelines for the best results
Use plain white or manila
USPS certified mail works best with standard white or manila envelopes. Avoid dark colors.
Leave label space
Ensure the front of your envelope has clear space for the certified mail label (approximately 4" x 6").
Security envelopes
For confidential documents, use security-tinted envelopes with a pattern inside.
Self-seal vs. gummed
Self-seal envelopes are more convenient, but gummed envelopes often cost less.