Mailers using PI permits with Non-Identical Piece Weights Must Converts to Seamless by April 1, 2026

February 18, 2026

Pub 401 and Manifest Mailing System (MMS) Retirement

Effective April 1, 2026, The USPS is retiring Publication 401 Manifest Mailing System (MMS) used for mail sortation and preparation with hard copy forms and documentation. Affected customers must migrate to Electronic Documentation (eDoc), Full Service, Seamless, and eInduction, for Letters, Cards and Flats by April 1^st,, 2026. The Quick Reference table below will be helpful in assisting customers determine their best option to continue mailing without interruption with the retirement of MMS.

Non-Seamless Mailers mailing Cards, letters or Flats using PI permits with non-identical piece weights must convert to Seamless by April  1, 2026 in order to keep mailing these types of mailings, according to the USPS.

Seamless Acceptance Fact Sheet:
https://postalpro.usps.com/mnt/glusterfs/2024-10/Seamless%20Acceptance_%20Mailer%20Fact%20Sheet%20_%20PostalPro%20v4.pdf