HTML emails are a very strange beast indeed. I spend a lot of my time each week writing them. Some advice: A table width of 656
works pretty well, and I wouldn't go a whole lot larger. I know that width prints on standard 8.5" x 11" paper well enough. We use it in all of our HTML emails and it usually renders well everywhere. We test on gmail, Outlook 2007, and the default mail application for OSX.
As @John mentioned Calibri is a Microsoft font, so it will only come through on machines that have it installed. Which should work out for you okay, as long as you also have a websafe back up available.
<table width="656" border="0" cellpadding="0" cellspacing="0">
<tr>
<td style="font-family: 'Calibri', Arial, sans-serif ;font-size: 11px;">Some content</td>
</tr>
</table>
Another HTML email pointer. If you add any <a>
and would like for them to not be the standard blue color, make sure you assign a style="color: #(color hex);"
for each one.
Best of luck. Writing HTML emails can be really frustrating some days.