Non machinable mail basically means that the mail cannot go through the machine to be sorted properly so it will need to be manually sorted.
Machinable mail is mail that can go through the sorting machines easily without much human intervention.
Machinable Mail is mail that can go through the sorting machine easily but non machinable mail cannot go through the sorting machines to be read and sorted.
Machinable mail will be able to go through the sorting machine where it can be read by the machine and computer and go through to the proper spot to where it can be delivered to the correct address.
A non machinable piece of mail would be mail such as a letter that has something inside it other than paper such as a pen or pencil, key ring etc.
The item inside the letter will make the envelope be irregular and bulge out which makes it non machinable so then a human has to hand sort it and they will stamp it as non machinable.
Non machinable mail usually requires a bit more postage than a standard letter would require.
A USPS machinable parcel is any package that fits within the dimensions of the USPS sorting machines which means that the parcel can be sent through and sorted through the USPS sorting machines which is a faster way of the parcel being sorted and delivered.
If the parcel is non machinable it means that the parcel is an irregular shape and cannot be sent through the sorting machines.
In that case the parcel requires hand sorting and hand canceling of the postage to get the parcel to where it's headed too.
Non machinable parcels are usually slower to deliver because of the extra steps required by a postal employee to sort it and find out where the package is going too.
So it's best to make sure your package or parcel fits within the dimensions of the USPS sorting machines guidelines so that the machines can sort the parcel and send it on it's way much faster.