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Question on P ATTR and B CODE and tray size determination in MailStream Plus

Product affected: MailStream Plus™, all versions, all platforms
Will MailStream Plus™ (MSP) use both MM trays and EMM trays if the presort contains two P ATTR mail piece dimensions, one for pieces that will fit into MM trays, and the other for pieces that require EMM trays?

No, MSP determines if EMM trays will be needed for any part of the mailing, and if so, then uses EMM trays for the *entire* mailing.

The way it works is that MSP first looks at all of the P ATTRs in the job, and determines which P ATTRs will be used based on any Input Name-Address records matching to them. 
As far as determining which size trays to use, MSP ignores any P ATTRs that do not have pieces matching to them.
If *any* one of the used P ATTRs exceeds the limits for using MM 'T' and 'H' trays, then EMM trays will be used throughout the mailing. 

Even if the P ATTR piece id is used as a batch code separator and you get, for example, two batches.  One batch having all pieces that will fit into T and H trays, and the other batch having all the pieces that require EMM trays.  MSP will still only use EMM trays for both batches.

The ALG LV parameter can be used to override the trays used in the mailings, but not by batch code.

For additional information on First and Second container information; please review
MailStream Plus™ Guide, the ALG LV parameter.
UPDATED:  May 23, 2019