I dealt with this issue a few weeks ago while setting up a new Mystic BBS. I decided to use an SSH proxy, current and well supported, that forwards the connection to the telnet port on localhost. Thus my BBS is SSH only.
It's at gitlab/dps8m/proxy
Yay! I'm glad other people are using this; it's awesome and updated often.
If you have problems with z-modem downloads, the authors added a switch (I think --no-filter) to stop the null characters from being ignored. You can also convert to utf-8 from cp437 with a switch. I have 2 ssh ports, one for cp437 and one for utf-8 because of that.
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Shurato, Sysop Shurato's Heavenly Sphere (ssh, telnet, pop3, ftp,nntp,
,wss, ssh utf-8) (22,23,110,21,119,999,2222) shsbbs.net FREQ Me!
*** THE READER V4.50 [freeware]
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* Origin: Shurato's Heavenly Sphere
telnet://shsbbs.net (1:340/1101)