You don't need to read everything for it to be useful. I get email reminders of things I need to do - I don't need to read past the subject line (same with shipping notifications), and purchase receipts are useful to keep in case there is a problem (you have a searchable record of when/where you bought it) but don't need to be actively read.

There's a high percentage of emails I get that I don't get any extra value from actually reading them, but I would lose value by not getting them at all.