Email Read Receipt
Some sort of "read receipt link" embedded in the email so that captains can confirm who has seen the email.
What problem are you trying to solve with this? The assumption is users on the team are expected to read their email.
Alex Grant commented
Other captains who we have introduced to Breakpoint have mentioned this feature a few times. Having an "email read receipt" in the App would allow captains to confirm that everyone in the lineup has seen the email and it would give the captains extra confidence that their team will show up. For me personally I have had a few players who don't use email all often and this would provide a simple way for me to check if I need to remind/ping people. I completely understand if this is not something that will fit nicely into the App, it was just something that multiple people have mentioned to me in the past.