Email address change notifications

Good morning,
on my www.remarpro.com site, I have a problem because the email addresses of our 3000 users have been changed via our CAS.

We use WP Cassify and I can’t see what other pluging could send these notifications.

Each time a user logs in, they receive the following email:
“Hello username,

This message confirms that your email address has been changed on the xxxx site.

If you have not performed this action, please promptly contact the site administrator at this address:
[email protected]

This message was sent to xxxxx

Sincerely,
The xxxxx IT team”

We are trying without success to deactivate this notification email, because most of the time, the user follows the instructions and contacts us.

I think this is not possible and I explored another solution: where is the signature line “XXXXX’s IT team” configured? I could indicate in it not to follow the instructions.

Thanks in advance