Without seeing your email HTML, it's difficult to tell what the issue is. Looking at how you described it, it sounds like you may have some coding issue when copying from external systems, which may not show in the Web interface of Marketo but do show up in email clients. Dreamweaver is great, but is not a scalable solution for emails and you'll end up with a lot of 1 off emails. Unless you're writing the text directly into Marketo, copying from other sources can cause issue, I suggest you copy your text into Notepad first then into Marketo via a token or editable region, that way all the formatting will be removed, test it out. If that doesn't solve your issue, then the issue may be you actual email template, make sure it's following general css support rules: CSS Support Guide for Email Clients | Campaign Monitor, Outlook is one of the most difficult to develop for, even PC and Mac versions work differently.