If you're business is like most businesses, the secretarial or administrative assistant pool is one big revolving door. People agree to work, but support positions at the bottom rung of the ladder are merely stepping stones to other positions in the company or to another company entirely.
There also is the matter of training every new person that takes the job.
How about forming a relationship with a virtual assistant? Virtual assistants are popping up all over the world, and serve in an efficient capacity because they only bill for actual time worked and the company doesn't pay any benefits.
What you e-mail is what you get - sort of. Make certain that whomever you agree to work with understands your needs and deadlines, and can match your working style.