Equivalent of "Dear Staff"

In my opinion, you can use these forms as an equivalent of "Dear Staff":

These expressions give a kind of closeness between the CEO and his employees.

In contrast to the terms: employees or even workers.

All of these forms are acceptable and wouldn’t make me raise an eyebrow, but :

‘Employé’ would feel a little weird, especially if some of them are in charge of others.
‘Collègues’ would be a little weird too because it conveys a thing of equality that you obviously don’t have with your employees if you are their CEO.

So I’d go with ‘Collaborateurs’ because everyone is technically, a ‘collaborateur’.

The ones I would avoid:

Mesdames, messieurs

for being too distant,

Chers/chères employé.e.s

because inclusive spelling can be considered to carry a political agenda, and

Cher collègues

because it implies the CEO is a peer the employees (already mentioned by beauchette).

I would probably agree with

Chers collaborateurs, cher collaboratrices

although I would have avoided it a few decades ago.

I guess I’d just recommend to start that mail with :

Bonjour à tous

Bonjour à toutes et à tous

Equivalent of “Dear Staff”