Outlook woes got you down? Join the club. (Meetings are on Wednesdays.) You might find that your mailing looks great in other email programs but there's a large space in Outlook or your mailing altogether crashes there. It isn't you — and it isn't us, either — but it is Outlook.
As just a bit of background on Outlook, while great at many other things, it can run into some trouble when it is asked to render an HTML email that has, for lack of a better explanation, too much code.
You can break a mailing and its code into two parts:
Content may need to be simplified in order to render properly in this email program. There are several things that can be done to simplify the HTML code. Whenever you have a lot of links, colors, fonts or other formatting, that's going to build up in the HTML and weigh it down. If you've pasted in text from another source (like a Microsoft Word document), you could be unknowingly pasting in other hidden formatting. (Try using our text pasting tool.)
When your mailing is likely coded correctly and working properly across all other email clients, you're fairly limited as to what can be done to get it to work in Outlook 2007 and 2010, where you're most likely to encounter Outlook's rendering limitations. Reducing the amount of text and formatting may help alleviate the problem, but then you're compromising the functionality of your mailing for just one program.
If the extra spacing is the only thing preventing you from sending the mailing, you can cut down on any formatting and links that may be unnecessarily contributing to the problem.
Outlook 2007 and 2010 in particular break content based on certain numbers of lines of content (based on Word's rendering engine). Instead of designing Outlook 2007 around Internet Explorer (a browser that's meant to translate HTML), Microsoft based its HTML rendering engine on Word. Because of that, several popular HTML email design elements aren't supported. Outlook 2010 uses the same rendering engine, which is why the issues carried over.
Fancy CSS (Read Microsoft's Outlook 2007 CSS support guide here)
Automatic text wrapping
Link styling (sometimes — 2007 and 2010 don’t support inline styles when the a tag doesn’t have an href attribute)
Padding (sometimes — 2007 and 2010 can change divs to paragraphs with nested span tags)
Image margins and padding
Rounded corners on buttons — Outlook 2007, 2010 and 2013 only support square buttons
Our proofer will alert anything over 40 KB, which is pretty conservative. Typically, anything under 60 KB is alright, but lighter is always going to be better in terms of delivery. However, Outlook 2007 and 2010 have a file limit size of 20 MB. If there's a huge image in an email, for example, that could cause trouble. The limit can be changed on your end, and we recommend setting it to 50 MB.
Due to the Word rendering engine, if there is an image where Outlook thinks there should be a page break, it adds the gap above the image. It's frustrating, but this explains why sometimes shifting content around will "fix" the issue, because it puts the page break in a different place.
Here's an article we've found that explains it and also one with some workarounds.
Oulook's engine has a maximum allowed height for images. They cut off, from the top down, anything over 1,728 pixels tall. We've always recommended that the largest image size you upload is 480 pixels in height or width.