I've built an html Email and used Google fonts.
I've included the fonts in the head tag using:
╔!--[if !mso]╗╔!--╗
<link href="https://fonts.googleapis.com/css?family=Oswald:200,300,400,500,600,700" rel="stylesheet"/>
<link href="https://fonts.googleapis.com/css?family=Merriweather+Sans:300,300i,400,400i,700,700i,800,800i" rel="stylesheet"/>
╔!--╔![endif]--╗
and to use the fonts, i.e I did so:
<tr>
<td valign="top">
<p style="line-height:1;margin:0;color:#ffffff;font-family:'Merriweather Sans', sans-serif;font-size:12px;font-weight:normal;">Für Fragen sind wir jederzeit für Dich da:</p>
</td>
</tr>
The problem is: the fonts are rendered perfectly on apple mail, on Gmail only Oswald.
I've tried to figure out, why 'Merriweather Sans' is not rendered correctly, but no chance.
Could you help me please?
For the first part of this question, apple mail supports web fonts. This is the reason you see it render properly across all apple mail clients.
For the second part (Gmail) would have Oswald in its family font, that is the only reason that I can think off that will render Oswald in your emails.
Gmail still has an issue with web fonts linked to emails and that is the reason 'Merriweather Sans' is not rendered.
Gmail does not work with Google Fonts or any webfont.
Gmail supports a number of web safe fonts. I can't locate the list and don't see Oswald listed. Perhaps it's supported, but not listed. Or perhaps it maps to a similar font.
Updated
These are the fonts supported by Gmail:
• https://jsfiddle.net/wallyglenn/g35nchmL/
For more information on fonts in email, check out the article below.
Good luck.
Web fonts don't have universal support, here are the email clients where they are supported:
According to this post on Litmus;
Which is why there is a comment on one of the answers about Roboto working on Gmail.