Issue PPPM-11248 // Your IMAP client does not appear to correctly implement Unicode messages

[rammstein]

Hello,

from time to time I have still some customers complaining about this warning message.

I'm using "Plesk Obsidian - 18.0.31 Update 2"

Your IMAP client does not appear to correctly
implement Unicode messages, see RFC 6855 - IMAP Support for UTF-8

I find the most interesting:

If I test it myself, I don't get the warning-message.

Testing with Outlook "Microsoft 365 MSO (16.0.13426.20270)" by putting "äöü" in the "mail-subject".
No error/warning or "Problem".

What is the exact function of the patch for PPPM-11248?
What did this change?

And is it "normal" that some customers / email-clients still have problems?

Has anyone had similar experiences?