Subscriptions

My company would like to build backup mail gateway. Do I need another license for this?

The rule is:

If the server will be active (turned on and used as a mail server etc...) then you will need an SNF license for that server.

If the server will be inactive (turned off, and/or no email passes through it) such as a "cold" or "warm" spare then you do not need an additional license for this server --- you will be required to move your existing license to the new server and remove it from your old server if/when the new server becomes active.

If you will have both servers active at the same time for any period then you will need a separate license for each.

The exception to this is when you transition from one server to another. In that case, you may use one SNF license on both servers, for a short, reasonable time as required. A "reasonable" transition time is considered to be in the range from a few hours to a few (2-3) days.