Learn English – Perhaps or Maybe or I Guess/Think – which one is correct in formal (office) email writing

If it's within your own company you can use simply "Colleagues,". If specifically your own team, then "Team,". (i.e. no "Dear" or "Hi" needed)

If it's not your place of work, then the usual "Hi" or "Hello" will do.

Using "one" when you want to address a person in general, not specifically the reader. This was considered good practice in general. Consider this:

When the stakes are high one is often tempted to cheat.

Verses:

When the stakes are high you are often tempted to cheat.

You might prefer the former to the latter because the latter comes across as very accusatory. This is really the only circumstance I will use "one" as opposed to "you." Generally, except in very formal writing, "one" comes across as rather pretentious or old fashioned. It puts distance between the reader and writer which might be a good thing, but often isn't.

As another commentator mentioned, often it is possible to rewrite in such a way as to avoid both. For example:

When the stakes are high, cheating is more likely.