how to integrate todosit with mail on the mac
Unfortunately, that's currently not possible, at least not when it comes to the free option to link emails to tasks as we don't have a plugin for Mac's Mail app.
However, with Todoist Premium, you could forward any message to Todoist's project directly and they would be converted to tasks with notes containing the email's body. This, however, wouldn't give you a link to this message.
Please check out this post on our blog in which we compare both options: https://todoist.com/blog/2013/01/zero-inbox-policy-with-todoist/