You'd think a Guild with 80+ members might have a second trustworth person that could help out with a storage mule.. as for the "SImplying the accounting" thing, it would be VERY easy to split up... One officer doesn Weapons and Armor, the other does the rest...... If someone mails an item to the wrong person, its a simple matter of resending it to the correct holder....
The Mail system is Burded enough without it having to keep track of items that should be in someones inventory or bank slots.