I still have several machines that interchange mail with each other and the Internet via uucp mailnet. I poll an ISP twice an hour (or use an alias to force a poll if i don't want the mail to wait.)
I even check my personal mailbox on that domain every couple months. (Every three weeks or so I get another offer to buy my domain name, which has been around since the list of machines that exchanged email fit on three typeset pages.) But you wouldn't BELIEVE the amount of spam that accumulates on an account that has been around since before the first mass mail-merge spam scripts were offerd for sale. (I think I still have a saved copy of that original piece of spam - advertising spam software.) The spammers STILL include that address in their mailing lists.
If the NSA or ISIS ever kills the connected Internet, UUCP mailnet will still work, merrily bucket-brigading email among the hadnful of machines whose mail transfer agents still interconnect by routes that don't just hand the mail off to an Internet hop.
Also: Back when we ran mailing lists over UUCP, the polling delay limited the deluge of mail when someone on the list accidentally forwarded his mail to the list. This gave us time to catch it manually and suspend the account before everybody was buried in repeated messages. B-)