"Snooze" to me implies delaying for a unit of time that you may choose to repeat. From their description of "Defer" it seems you pick a specific date/time and add it to your calendar.
verb (used without object), deferred, deferring.
1.
to yield respectfully in judgment or opinion (usually followed by to):
We all defer to him in these matters.
Defer forces you to book a time in your calendar instead of "snoozing" the message just so that it reappears later. Actually, snoozing was one of the most exciting features I saw in Mailbox, but after using it heavily I realised I get plenty of messages on Monday morning back to inbox and I just snooze them again. It turned to be a complete disappointment for me
How about making "defer" be snooze with a hard limit of 2 or 3 times max?
This I think would work because you could snooze if really you cant/dont want to deal with a message immediately but eventually you would have to.
Or maybe have up to X "snooze slots" so that you cant snooze everything and you snooze things that truly dont deserve to be deleted. And you would have to empty a slot by dealing with a snoozed message to be able to snooze a new one.