USPS Local Post Office Postal Clerk has refused to accept my legitimate mail in the Flat Rate Priority Envelope Euclid, Ohio

There is probably something more going on here, and I wonder if the OP would update the situation.

Because people don't usually just quote DMM rules, the OP must either do a lot of shipping or they don't do any and were trying to find a loophole to save on postage.  A picture of the envelope in question probably would go a long way, or at least what you were mailing.

However, you are technically correct.  As long as the envelope is not modified they are "supposed" to accept it.  Now, this means NO modification.  Even a piece of tape to secure the envelope shut could technically be considered "modified".  Because it could be seen that the flaps did not close securely on their own.

As other people suggested, if one Post Office says No..go to another one and try it with them or use other packaging.

This whiner feels she has the position to tell a post office what to do with there own product?? That envelope is the property of USPS and the USPS has the right to dictate how it is used. Does this complainer feel the need to go into other businesses and tell them how to interpret their coupons, what the manufacturer's maintenance schedules will be for the car warranty, that the shipping company should approve a damage claim when newspaper packing was used, etc, etc?

A post office, like any business, reserves the right to dictate how their own products and services are used. If there were enough people that complained that they could ship a flat rat envelope that was stuffed to look like a beach ball, then perhaps USPS would put a disclaimer in that the envelope were designed for paperwork and flat items.

As the previous responder stated, why not use a flat rate box? Was this complainer to cheap to pay the small difference for a proper container? Is it really that big of a deal that a rampage needs to be performed in order to tell the post office how they better do their job with their own products? If this complainer tries printing her own label at home and sends it through that same post office, it likely will be sent right back to the return address for a valid reason.

UPS and Fedex require paperwork only in their envelopes for the same reason USPS intends the envelopes to remain flat. If that USPS envelope is allowed to bulge, a percentage of them will burst and contents will be lost or damaged. No doubt this complainer would then also file a claim that the postal service was at fault.

It seems rather ludicrous that the Attorney General will order any company (let alone the USPS) to actually allow flat envelopes to swell to any size. I beleice the Attorney General has better things to do than to accommodate irrational and petty tantrums for a unique individual who is trying to save pennies.

Could this whiner be the same person that was expecting USPS to ship a 4 month old puppy in a flat rate box? The complainer also said she would file a complaint for a refund. Well too bed for her. The courts said 'no refund' AND 'no puppy back'. Oh that USPS and their silly rules that customers should be able to modify whenever that feel like it...

That clerk is an idiot.

File a complaint with the POSTAL INSPECTORS.

Or, bypass the counter. Print your own label and postage online and then drop it in the mail collection box. See what happens.

Or, switch to the small flat rate box for the same price.

Lots of options here.

FYI...Your State AG has no jurisdiction in this matter.