The thing is Reverend is not a title, it is not used like 'Dr' for example. It is in fact used in pretty much the same way as 'Honourable' for Members of Parliament. So next time you use it in conversation do the MP check in your head. I haven't checked how to email an MP, but let's get to letters.

A letter to a Vicar would be addressed to:
The Rev'd Lucy BruceAnd begin
The Vicarage
Great Smallding
Cranchestershire
Dear Ms Bruce,However an email has no way of indicating the orders of the clergy-person being written to. Vicars themselves should have no problem with this, but some people writing to Vicars obviously do. Otherwise they would not have asked the question on Twitter.