It seems that I did not accurately disclose the meaning of my message. I mean what your UNIVERSAL letter link to yourself looks like, by clicking on which ANY user will go to the message to themselves.
a) If I wanted to use the link only for myself, I would make a link like this:
https://mysite.com/new-message?username=ADMIN&title=Title
b) But I want to make a link for everyone, so that everyone can go to the letter to themselves, and not to someone else, for example:
https://mysite.com/new-message?username=ME&title=Title - THIS DOESN’T WORK
c) My alternative solution is a letter to a simulated user, for example “Bot - draft”:
https://mysite.com/new-message?username=BOT_DRAFT&title=Title - this works and each user can send a letter to this bot and consider this action as a personal message to themselves.