@ems_sports_cards
Did any of your envelopes contain top-loaders?
One of the main problems with the eBay Standard Envelope (ESE) is when sellers attempt to mail cards inside a stiff top-loader -- most of the time, the top-loader is too stiff and rigid to quickly pass through the USPS high-speed rollers in the sorting machines: if the ESE is too rigid, the ESE will jam the machines, and get kicked out. Then the ESE is considered to be "non-machinable," and may be returned to the seller marked "insufficient funds" -- although (worst case scenario) sometimes the ESEs are delivered to the buyer marked "postage due."
(And apparently some "non-machinable" ESEs just get sent to the "dead letter" department.)
Also -- never take the ESEs to the post office counter for mailing! Many USPS employees are unfamiliar with ESEs, even though the ESE is legal, contracted business metered mail. But some USPS employees have been known to refuse to accept them, believing that they are "phony" or "counterfeit," and the employees will attempt to charge you for a full USPS Forever stamp.
And some USPS employees have kicked the ESE problem to a supervisor, who may also refuse the ESE, or even just "set it aside", for "future investigation."
Since the USPS counter employees are unable to "scan" the ESEs anyway (their hand-scanners are unable to "read" the ESE codes), just avoid handing the ESEs to ANY counter employee, and drop the ESEs into any of the USPS "blue" boxes; or (best scenario!), if there is a "Metered Mail" slot in your post office lobby, drop your ESEs in there -- using either method, the ESEs will be mixed in with other outgoing mail, and be delivered later that day to the next USPS Distribution Center, where they should receive the initial "scan."
As long as your ESEs have received at least one "scan," you are covered for insurance purposes for "lost" or damaged mail.
Good luck with Em's cards!
KrazzyKats • Volunteer Community Member • 
