First let me apologize for the repeating answers prior to this. I don't know how that happened.
Anyway, I know a little about bulk mail acceptance, but very little about mail processing. From what I am told by plant when I have complained about getting carrier routed mail in tubs or, if we are lucky, by themselves in a tray, is that the plant is trying to run it in DPS but fails to get a quality product. Either the mailing is jamming up the machines, or is not sorting well and degrading the quality of the DPS, resulting in a very poor DPS product.
By then, they have already broken open the mail and made a mess of it (it is mixed up and co-mingled with other routes and even other offices). So their choices are to carrier route it on the DPS machines, or if there is not time to do that, run it on the flat sorters to at least get it back to carrier routed.
When they sort the mail in DPS they are in the mindset that the mail is going to city carriers and they are going to try to run it in DPS if at all possible.
Many times, after getting what appears to be mail perfectly suited for DPS in a tub or tray, we complain and/or sent the mail back to plant for reprocessing only to get it back in even worse shape than before. The plant told me that if we ever get it in a tray or tub to not waste time sending it back because We would not have received it that way unless they already attempted to run it in DPS.
Anyway, that is what they told me, but I would not swear that it is true, but it sounds logical to me.
