Watchlist notification emails contain the username/IP of the person who has edited the watched page. This means that in cases where an editor has accidentally edited logged out, any user receiving watchlist notification emails for that page now has a permanent record of the IP address of the editor, even if the editor immediately realizes their mistake and has their IP address suppressed onwiki.
IP addresses are listed in two places in these emails: first, the prose summary ("The Meta page $pagename has been changed on $date by anonymous user 184.108.40.2069, see $link for the current revision."), and second, the "contact this editor" links later in the email ("Contact the editor:
mail: No email address
While release of an IP in this way is a low-priority issue in many cases, in cases of hotly contested or highly-watched pages (for instance, Gamergate articles, which involve an internet-wide dispute that has gone offline into real-world threats in the past), this is potentially a significant issue for users concerned about their privacy and security.
Please consider anonymizing IP addresses in these emails in some form - possibly by changing the email text to "has been changed on $date by an anonymous user" and removing or obfuscating in some way the link to the IP's talk page.
Per Quiddity, the current wiki-config variables for these emails are listed at https://www.mediawiki.org/wiki/Manual:Configuration_settings#Email_notification_.28Enotif.29_settings