Punctuation after salutations and complimentary closings

Is comma typically required after salutations (e.g, Dear Mr X) or may they be also omitted in letters and emails? What are the official standards in BrE today and what are the trends? I've understood that the trend is towards omitting the comma.
Information found in the Internet is ambiguous, e.g, BBC/worldservice/learningenglish/grammar/suggests that no punctiation is used after salutations, but Usingenglish/articles/letter-writing suggests using the comma.

[Tdol]

The comma is often omitted, but I would use it in a formal letter.