When someone offers to make an introduction on my behalf or - as is more often the case - I ask someone to make an introduction on my behalf, I often write the intro email myself and email it to the introducer, suggesting that they use it as a template.
I do this because:
- It lets me control the message somewhat and ensure that it is short/accurate.
- It saves the introducer a few minutes of writing.
- It just seems like the right thing to do, even though people don't usually expect it.
Do it. People will use it. And you'll be glad they did.