Better message/e-mail sync between mobile app and web app
One of the major complaints I have about your otherwise excellent product is that message notifications on the mobile app aren't updated if I read, delete or archive the e-mails via the web inbox.
For example, if the mobile app notifies me of a new e-mail and instead of reading it on my smartphone, I go to the web and read it there, the mobile app notification doesn't acknowledge that. I have to read or manage the e-mail on the smartphone even if I already read it on the website. It's makes for a lot of unnecessary double work.
This is an annoyance for me as well, as I have to clear the notification from mobile or check if it's a separate message. Seems trivial until you do it 20+ times a day. I need to sign in, do 2FA; just to find there's nothing new.