Yes, it is probably deductible. No, there is no allotment unless you travel. There are per diems for persons who must travel for work.
To be deductible, a business expense
must be both ordinary and necessary. So, if your mailbox rental is
ordinary (common and accepted in your trade or business) and necessary (helpful
and appropriate for your trade or business) you can claim it.
An
expense does not have to be indispensable to be considered necessary.
See the screen shot below.
