Determining the difference between MM and EMM, T, H, and E trays in letter mailings and when are each used using MailStream Plus

Products affected:  MailStream Plus™
By default, MailStream Plus (MSP) will use the correct trays for letter presorts.  

There are three sizes of USPS letter trays per the Domestic Mail Manual (DMM).  They are described in section 203 5.2 (as-of the current DMM in April 2019):
  • a. 2-foot managed mail (MM) trays: 21 inches long by 10 inches wide (inside bottom dimensions) by 4-5/8 inches high.
  • b. 1-foot MM trays: 10-1/4 inches long by 10 inches wide (inside bottom dimensions) by 4-5/8 inches high.
  • c. 2-foot extended MM (EMM) trays: 21-3/4 inches long by 11-1/2 inches wide (inside bottom dimensions) by 6-1/8 inches high.

The first two trays listed are MM trays.  These can hold letter mail up to 10 inches wide and 4 5/8  (4.625) inches high.

When a '2-foot' tray (really only 21 inches long) is used by MSP, it is indicated by a 'T'.  For example, on the Audit Trail report, you might see a line like:
  • PS T-Tr 1
When a '1-foot' MM tray (really 10-1/4 inches long) is used, it is indicated by an 'H':
  • PS H-Tr 1

When the mail is being put into MM trays, whether a T or H size tray is used is determined by whether the mail to a single presort destination will fit into a T tray, or an H tray, or if it needs a combination of the two sizes.

The size of the mail piece in a mailing is indicated on the P ATTR parameter.  The length in positions 36-40, and the height in positions 42-46.
Using the dimensions as defined on the P ATTR parameter, when a letter mail piece exceeds either the the 10 inch width(length), or 4-5/8 inch height limit, of a MM tray then (by default) MSP will use EMM trays.  They are indicated with an 'E":
  • PS E-Tr 1
There is only the single EMM tray size, with a length of 21-3/4 inches.

If there is more than one P ATTR in a job, and some pieces meet the MM size limits and some pieces exceed the MM limits, the whole mailing will be prepared in EMM trays.

At the beginning of this text, it was mentioned that MSP uses the correct tray sizes *by default*.  That can be over-ridden by using the ALG LV parameter position 14 and 16, to indicate the tray type to be used for the First and Second container level.
Why would this over-ride ever be used?  The DMM gives example situations:
  • Subject to availability of equipment, standard 2-foot MM trays must be used for all letter-size mail, except that EMM trays must be used when available for letter-size mail that exceeds the inside dimensions of MM trays defined in 4.2.
  • When using EMM trays, the 1-foot MM tray may be used in order to minimize the number of letter trays.
  • When EMM trays are not available for those larger pieces, they must be placed in MM trays, angled back, or placed upright perpendicular to the length of the tray in row(s) to preserve their orientation.
Basically it relates to tray-size availability.  In such situations ALG LV could be used to tell MSP the actual tray size(s) being used for the mailing, so they can be filled accurately.
UPDATED:  April 17, 2019