"from June onwards" or "from June" or "on June"?

Question

1. I will be transferred to another branch from June onward.
2. I will be transferred to another branch from June.
3. I will be transferred to another branch on June.

Which one is correct?

Answer 1

I will be transferred to another branch from June onward.

Means that you will be transferred from(starting) June and all the months following June.

I will be transferred to another branch from June.

Technically that the branch comes from June, but most people would understand that you mean that you will be transferred from(starting) June and all the months following June.

I will be transferred to another branch on June.

Is incorrect, you could say:

I will be transferred to another branch in June.

Which means that in June you will be transferred.

Answer 2

The comment that said "starting in June" was correct.

If you don't know the exact time frame you'd be at the branch you would just say "in June". The "onwards" is kind of implied in this situation so you don't really need to say it. And the phrase "until further notice" would probably be better than "onwards" in that situation. Both mean the same thing but I rarely hear people say "onwards" in English. If you knew you were going to the branch in June and leaving in September you could say "I'll be at the new branch from June to September."