Technically you can use any font in your email signature.

However, unless the receiver of the email has that font installed also, they will not see the email signature the same way that you intended it to be seen.


Best practices

Use a 10-point standard Windows font with fallback font for Mac as show in below example.  

Non-standard typefaces and HTML will not translate well across email clients.


Example - Arial 10pt on Windows and Helvetica 10pt on Mac:   

<font face="Arial, Helvetica, Sans-Serif" color="#000000" style="FONT-SIZE: 10pt">Arial 10pt (Win) or Helvetica 10pt (Mac)</font>