Whenever you are writing about an action that the company, or a department, as whole is taking, use ‘we’, and whenever it is you personally taking the action, use ‘I’. In the examples above, the first is an action on behalf of the company, and the second is an action taken by you personally. “I will talk to my colleagues” is correct in that case.
When writing in a business style, you should do so in such a way that there is no possibility of ambiguity, and that your message is clear and easy to understand. Don’t make the mistake of believing that senior personnel in your, or any other, company is educated and can understand the nuances of vocabulary, grammar and punctuation. Most can’t. Most business leaders are not English language majors. All they want is clear writing that they can understand without having to reach for a dictionary. They also want clear information, and never make excuses: provide reasons.
“Dear Mr. Customer, I am sorry that your order is late. It will be with you shortly” is not acceptable, whereas “Dear Mr. Customer, We apologize for the lateness of your recent order. It was held up due to a problem with our production unit but will be with you by the 17th of this month” is more acceptable.
Business letters should never tell lies or prevaricate. They should be short and to the point, and make an honest statement of the facts. Lies and prevarication have a habit of biting you later, so leave them alone. Put yourself in the position of the person you are writing to and write accordingly.
Business letters relevant to internet businesses are no different, only that you must not assume that just because it is the internet then you need not be so formal. Many internet entrepreneurs are very educated people who run their internet business in the same way that offline businesses are run.
The best approach you can take when writing a business letter relating to either an online or offline conventional business is to stay formal, do not use too many long words and keep to the point. State what has to be said and no more. Businessmen want the facts, not the waffle.