From #128#issuecomment-313331723

Would it be an idea to have the unsee_collected_alerts split into which receiver they are for? As it is right now it's just a total number of all alerts received for the system, but adding the receiver as a dimension would allow different teams using the same Alertmanager instance to dig into how many alerts they currently have going off.

Seems like a good idea, but current code doesn't make it easy to add.