I agree with @Courtney. As long as you keep it a short punchy sentence you should be good. That's what we usually do as well.
Try setting a max-width: 100% attribute within the style..
This is what we use and works absolutely fantastic:
width="71" style="width: 100%; max-width: 71px; display: block; border: 0;"
I think that this is probably something that will hopefully soon burn out, as (hopefully) companies (like gmail) will start implementing better filters for what's spam and what isn't.