with 2.5.1 my users reported that they received invalid emails. Here's the first one, it contains a pass word reset link, which is broken and if they click on it they land on an error page, of course:
Then I went to the dashboard and changed the default email format to HTML, which results in such mails:
I looked into the template for this mail, that blue rectangle on the bottom is supposed to be a button. The users don't even think about clicking this and click on the forum link above. Unfortunately this doesn't lead to the pass word reset page, so they need to repeat the process, receive the same invalid email, and so on.
Also note the various other rendering errors, invalid umlauts and scattered equal signs here and there. In one case the email has been blocked by the enterprise mail filters because of this.