I have a very quick and efficient method of emailing, set up using my email program's signatures. As soon as payment has been received, I retrieve eBay's end of auction email, click on the buyer's email address, then select the relevant signature from within my email program.
Here's the actual signature in full:
Hi [__add in their first name__],
Thank you for your speedy payment – much appreciated. I'll post the item today, and it should be with you on Monday Tuesday Wednesday Thursday Friday Saturday. [__delete ones not appropriate__]
It's well wrapped and boxed, and should arrive safely. I hope you'll be pleased with it.
I will leave feedback for you, and trust you will do likewise for me in due course. Many thanks.
This little note is a point of contact between me and my customer. Many people have commented on 'good communication' in my feedback rating, so it must have been well received.
I have similar signatures for multiple items, and ones for overseas customers.