Dear Mrs A D:

You wrote:
> I note that on your website you advise that the greeting in a business
> letter always ends in a colon but any business letters I have received the
> greeting ends in a comma ie Dear Mrs Dudley,
>
> Please advise
>
Is it done differently in the UK? Colons are standard in business letters I receive. Occasionally an advertiser will use a comma to make a more personal appeal.