We receive emails for every change of a article listed in watch list. Here the problem is the article URLs are written in Percent-encoding. So it is not possible to read that and it looks bad in the email body. Sometimes it requires 4/5 lines to show the name of the article.
Along with this there are some formatting issue which exists from the beginning and not resolved for a long time (T58063). The emails i receive form the 'MediaWiki message delivery' system are properly formatted. I am not sure which application is used to format this emails but the default Mediawiki emails have some issues. You can check the screenshot here to get an idea about the problem, https://nimbus.everhelper.me/client/notes/share/74770/w8BbZLSEFp9gVhZZ1GAdrcfL6aG7AvVf/ .
See Also: T65577: Create a "Watching and notifications" tab in MediaWiki core