Hi @gsmith
Thanks for your answer.
You are saying to do something like this?
The problem is that, even with that, Graylog don’t add the additional part of the title (the aggregation) to the subject of the email:
The only thing that I can think of to put the value of a field in the subject of an email, is to use the HTTP Notification on Graylog, and make a webhook to get the information of the alert with and automation tool, and send the email with that, but I think that the feature that we are talking about is pretty simple to be available at Graylog, 
Sadly I’m not a Developer.
Thanks again for your help @gsmith
Regards,
Alejandro