Sending, receiving, and organizing email in Outlook.com
@larry loois said
safe senders in mail are not saved
This is an ongoing issue for some users. No direct fix for the inability to save a new entry in the Safe Senders List.
One Workaround is to add the email to your Contacts. See the Answer by "Hornblower409 Sep 5 2026" in
https://learn.microsoft.com/en-us/answers/questions/5989552/couldnt-save-changes-when-unblocking-an-email