Recommended sizes for email signatures when design in Photoshop?

Hello,

Can someone tell me what are the recommended settings (width, height, resolution), when you using photoshop to design an email signatures.

I searched online and some sites says 72 pixels per inch…

I did it and saved it with different format (JPG, PNG, GIF) then export it into my mail (Incredemail) and the quality is poor and is too small.

I am making / designing one for my workplace but I really want to achieve the quality of the design when I export it into mail (outlook, incredemail, etc).

And I will put it into my colleagues work as a standardized – email signatures for everybody.

Again, can someone help me to achieve this (right settings for this)