How do I start an invitation email?

I am emailing some co-workers to invite them to a celebration I have organised. What would be the first sentence/sentences I can use? Other than "Please join us in celebrating...".

How do I start an invitation email?
you can start it with something like"we cordially invite you for a little dinner organised for "so and so" occasion.....
Reply:I don't know.
Reply:contact me to tell u!
Reply:Stop feeling sorry for yourself and join us!!!!!!!