A Linux server sends email to "root" by default. Rather than hardcoding an email address into every config file, it's cleaner to simply place a file named "forward" (that's dot-forward) in the root directory of the root account. The contents of that file should be a single line which is the admin's real, outside email address.

Now, whenever any process sends a message to "root", it will be automatically forwarded to the address specified in the ".forward" file.

The file should be a plain text file, with permissions 0644.

Lastly... put "root" back into the "mdadm.conf"  file if it's been changed.