Hi everybody.

I've got a question about the opening task of a letter.

Americans often start this way:
  • Hi, Peter.
Question: Is this way also in the UK correct? Or do they leave the comma and the point or not?
That would be a very informal letter so I'm not sure you need to worry too much about 'rules' anyway (are you sure the US would finish a salutation with a full stop?).

Hi Peter,

is the form I would think is most common in the UK to match with the more formal 'Dear Peter,'
Well the letter is very informal. And yes, the American write it with a point in the end!
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This American would say:

Hi Nona,

Hello Spinnaker,
Sure? Someone told me to set a comma!
I think the American style is often to complete a salutation with a colon : but not a full stop.
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Yes, just so, in a business letter, we would use the colon.

Dear Ms. the'Brit:

Dear Mr. Spinnaker:

But the full stop is not right.
OK! And what's about the comma after hi?