I've heard that using "Hi" in business correspondence is acceptable even if you email a person for the first time (I also can see "Hi" from people who email me for the first time), but I usually use "Hello" in these situations, not to seem familiar. So, are there any issues with using "Hi"? or it is better after all to use "Hello"?
My feeling is that you would normally use "Hi" only in certain cases, and in these cases "Hello" would also be acceptable.
Using "Hi" implies that the person you are writing to is already in some way expecting you to contact them, or at least that they should not be surprised that you are doing so. This could be because:
- They already know you.
- You or your company have an established relationship with them, for example if they have contacted your company about some issue and you are replying to them about it.
"Hello" would also be acceptable in these cases.
On the other hand, if you are writing to someone with whom you have no relationship and who has no reason to expect any correspondence from you, then it is much better to use "Hello."
This mirrors what would happen in an in-person encounter with a stranger. "Hi" is reserved for cases in which contact is expected - for example, you are a customer approaching a receptionist (or vice-versa), or you are approaching a stranger with whom you have made eye contact in such a way that a verbal exchange appears imminent to both parties. You would not use "Hi" with an unknown passer-by on the street if they had not yet noticed you.