[Using Mailchimp] I want mobile to render desktop version

While I'd argue against forcing a desktop view on mobile for the sake of your subscribers, you could kill the responsive stuff in the email template. Assuming you're familiar with HTML and CSS, you can edit the template's code to remove mobile-specific media queries and convert any fluid tables (tables using percentages for widths) into fixed-width tables (using defined pixel dimensions).

Before you do so, you should get a baseline of where your audience is opening their email. If you have a largely mobile audience (which is increasingly the case for most senders), I'd leave all that responsive goodness in there. It's tempting to design and send campaigns tailored to your own tastes, but really, it's what your audience wants that really matters.

Daniel,

If you're using MailChimp's native templates to create your campaigns this can be tricky. They don't have a way to view their full HTML/CSS code outside of the individual drag/drop content blocks. I even tried to save one of the campaigns as a template, and I still got the same drag/drop WYSIWYG editor.

If you absolutely have to have desktop layout, you could insert a 560 x 1px spacer image in each of the content blocks. Simply open up the Source view and insert your <img> tag at the top or bottom with the min-width:560px property. However, when I sent a test to my Gmail account it did funky things, so I don't think this is a bulletproof fix.

I would strongly heed Jason's advice - find out what your audience is using. Unless you have a very low open rate for mobile (like <10%), then you should absolutely use responsive code, regardless of whether you like to use it or not.

If you're still insistent on going with a desktop view, then I would recommend coding your own template with the 560px spacers inserted in their own table rows and use that for all of your campaigns. At least you'll have access to your own code and can tweak as necessary.