Soapbox Mailer uses Long Text-Area fields to store the HTML for both the Email Templates' HTML as well as the Campaign's Edit HTML Body and Edit Text Body content. The size limit on these fields is set by Salesforce to 32,768 characters.
What if I need more characters to fit my Email Template HTML?
While we can't expand the size of this field at this time, you can save quite a bit of space by simply removing extra white spaces. Here are a few free tools you might want to use to compress the number of characters used by your Email Template body HTML (note: none of these have been created by PICnet, use at your own risk):