Just so we are on the same page …
I went in iy...international..org.
On the email settings page, the SMTP username cannot be changed, or it won't log in at all.
In the "From" field of that same settings page, I switched from "iy...international.org", which was the name when I sent them the tests, to the one they suggested, which is "support@iy....international.org".
I then created a mailing and sent myself a preview.
It came to me with the usual default from name and address of K.... B...., firstname.lastname@example.org"
In other words, it failed to properly recognize the From Name as per usual.
Did I miss something I should have done? Is that what you implied?
Please advise if I have made an error.