On March the 1st I changed my Wikipedia email address and since then I haven't received any notification when a page in my watchlist is edited.
For context, the user has switched back to his former address, and is still unable to receive said notifications.
He was able to receive direct email (via "Email this user") on both his mail accounts, but he can't receive other notifications on the one he means to use. He also couldn't receive Phab-related email.
Trizek, yes, he hasn't changed anything there AFAIK, and all the email boxes are flagged.
Actually he did switch from HTML to the other setting, but that was after the problem was confirmed (so this move didn't seem to help or to make any difference).