The default email footer setting is:

You have received this notification because you have either subscribed to it, or are involved in it.
To change your notification preferences, please click here: http://hostname/my/account
This setting can be changed from Settings -> Notifications -> Email footer.

This approach have several issues:

• the text can be removed by an admin
• the text is not translatable
• the text is too generic and the user cannot understand why he received that notification

My proposal is to replace this text with the real reason of why the user received the notification. In this phase, I propose the following reasons with the according translations:

| Reason | Message | Details |
| @SUBSCRIBED@ | You have received this notification because you have subscribed to it. | because he is subscribed to that event |
| @INVOLVED@ | You have received this notification because you are involved in. | the user is either author, assignee or previous assignee |
| @WATCHED@ | You have received this notification because you are watching it. | the user is a watcher |
| Admin Redmine@ | You have received this security notification because you are an administrator. | the user is an admin and he received a security notification |

In the future, we can add the @MENTIONED@ reason (#13919) to cover the case when a user is mentioned or even a more granular reason for the involved reason: author, assignee or previous assignee.

Also, I propose to always display the text "To change your notification preferences, please click here: %{link to my account}."

Below is an example from a security notification with both messages (first message is the new one; second message is the old one).
!{border: 1px solid grey; width: 30%}sn.png!