Inbox zero is a treadmill. You win it every morning and lose it every afternoon. The durable goal is different: a queue where most items arrive already sorted, and your job is supervision rather than processing.
Sort by decision, not by sender
The first pass should group mail by what it needs from you: a decision, a draft approval, a quick fact, or nothing. An assistant can do this pass completely, because sorting is reversible and cheap to correct.
Draft everything that has a pattern
Scheduling, acknowledgments, status replies, intros. These replies rhyme. A draft library tuned to your voice turns most of the queue into a review pass measured in seconds per item.
Protect the exceptions
The value of delegation is that the rare, important message gets more attention, not less. Flag anything from a list of VIPs, anything with legal or financial language, and anything whose thread ran long without resolution. Those stay at full manual depth.
Measure what changed
After two weeks, count the messages you personally typed versus the ones you approved. Most people find the ratio moves faster than expected, and that the review passes stay sharp because the volume per item is low.
The endpoint is not an empty inbox. It is an inbox where nothing sits unprocessed because everything has a lane, and the lanes mostly run themselves.