BF> I really do want to keep my port 23 open, so that my users can telnet to
 BF> my BBS.

I don't have port 23 open to mailer/bbs anymore but I have a fake prompt
in Xenia Mailer:

 BF> + Xenia Mailer 1.98.06+ OS/2 (SN:399USBJ14); Node 2:221/360@fidonet -
Task 2
 BF> + COPYRIGHT (C) 1987-1998 by Arjen G. Lentz & LENTZ SOFTWARE-DEVELOPMENT
 BF> + This copy is licensed for use by: Tommi Koivula

 BF> Hit  twice for BBS.

 BF> OS/2 Login:

And for login attempts as root, admin, sysop or shit like that the
mailer just disconnects without loading the bbs.

'Tommi

--- Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:54.0) Gecko/20100101 SeaMonkey/
 * Origin: SmapiNNTPd/Linux-Pi 1.11 (2:221/0)