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[holsteinatlanta]

I have Endicia and a Zebra printer and always send DVDs and CDs either medial mail or first class package.  Was wondering what first class flat envelope without tracking is and when can I use it?  I wouldn't use it for items that I wasn't afraid to lose.  It I sell a cd for $5 with free shipping, media mail is $2.75 and flats are $1.60.  

Is  tracking the only difference? 

[nobody*s_perfect · Accepted solution]

No, you can't use it for DVDs or CDs, since USPS requires that envelopes sent as "flats" must be flexible.

Your item can be mailed as a letter if the weight is not over 3.5 ounces, and the thickness is not over 1/4 inch.

https://pe.usps.com/text/dmm300/201.htm#ep1096318