Steffen Kaiser writes:

let's put aside the question, if this way is sensible or not.

[... continuing in nonsensible mode ...]

And if you are at it, maybe a dummy server with a self-made script that returns "+OK POP3 your IP is ....", then return +FAIL for any further command.

Been there, done that (for a different problem). Not all mail readers will show you banners; to make this really work, you have to implement USER and PASS (accepts anything), STAT and LIST (one message available), RETR (dump your informational message payload), QUIT (disconnect), maybe TOP, and everything else is an +OK no-op. I patched Qualcomm's qpopper to do this.

As to whether the OP *should* do this, definitely not. Find a better solution.

Joseph Tam jtam.home@gmail.com