My inbox is my todo list. If I want to go nuts I can add a “waiting for them” label. Archive means done. Unread means unprocessed. I can send myself an email or if the task originates from someone else their email thread is the task. For voicemail, call, SMS heavy workflows of the past I routed my sms and voicemail through my inbox as well. This tooling is very personal but the above I’ve found to standup to very large workloads.