I have a question regarding some valedictions in emails. As you know, “Yours faithfully” and “Yours sincerely” are sign-off phrases primarily used in British English.

These are the generally accepted rules to go by:

- When we start an email with “Dear Sir/Madam”, i.e when we don't know the name of the recipient, we should end it with “Yours faithfully”.

- When we start an email with “Dear Mr + Surname”, i.e when we know the name of the recipient, we should end it with “Yours sincerely”.

These rules can be found in Fowler’s Dictionary of Modern English Usage, Oxford Handbook of Commercial Correspondence and other dictionaries as well.

The problem is that I have come across some rules stating that, we can use “Yours sincerely” at the end of an email, only when we know the addressee to some degree (having met that person in real life, etc).

So, my question is - Can we use “Yours sincerely” as a valediction when we know only a recipient's name but does not know the recipient in real life? If not, what other formal expressions should we use instead?