I like to be able to link to my mail. Apple gives you a way to do this, but you have to open the raw message to get the messageid. I finally decided to create a workflow that would allow you to get the message id's of selected mail, format them and put them into the clipboard.
The workflow works like as such.
Select message or messages in Mac Mail app. Open Alfred and type mailurl. optionally type a format html or markdown (md). If no format is selected html is assumed. Paste messages into markdown or html sensitive application.
It is probably worth noting that this is useful in a variety of situations. I use it to link email messages in Things, DayOne, and Calendar. It is great to be able to reference the email the todo, calendar event, or log entry that created it.