Formatting and fonts changing after email campaigns are sent

Formatting and fonts changing after email campaigns are sent

Hi,

I have had difficulty with formatting and fonts changing after an email campaign is sent.  During sending test campaigns my colleague even had a different colour font come through for some body text.  This is most noticeable in a subheading and the email received by my colleague looks very different to what I received on test.  Are there any fixes? Quirks that once known will stop this form happening?