The trick is to save your campaign as a new template and then export it.
- After logging in to your MailChimp account, go to Campaigns and open the campaign whose HTML mailing you wish to export.
- Click on the green Save To "My Templates" button at the top left.
Name the new template file appropriately, or accept the campaign name by clicking "Save As..." It would be best if you were to replace any letter spaces in the filename with underscore characters, before saving it. - Click Save & Exit in the top-right corner and select Dashboard.
- In the left column, click the My Templates button.
- Under the Select a Template Option, click the Select button under My Templates.
- Rollover the desired campaign template thumbnail image and select the gray down arrow which appears (a mouse tooltip might display Export this template). Save the template HTML file to your local hard drive when prompted.
Done!
You might want to add your subject line between the <title> tags near the top of the code. (MailChimp puts their own tag — *|MC:SUBJECT|* — in there by default, which you'll need to replace, though ultimately your partner will set up the mailing as they require.