This is related to how Microsoft Outlook 2013 renders HTML and CSS. The same email may appear correctly in Microsoft Outlook 2010.

In order to resolve the display discrepancy with Outlook 2013, add the following code to the <table> tag that houses the image:
  • style="mso-table-rspace:5pt;border-collapse:collapse;border:1px solid #ffffff;
For example:

<table align="left" border="0" cellpadding="0" cellspacing="0" style="mso-table-rspace:5pt;border-collapse:collapse;border:1px solid #ffffff;">

Disclaimer: Blackbaud provides programming examples for illustration only without warranty either expressed or implied including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose. This article assumes you are familiar with HTML/CSS/ and the tools used to create and modify this code. Blackbaud Customer Support may help explain where the code should live in the product, but we will not modify or assist you with modifying or troubleshooting these examples.

Please note it is always best practice to make a backup the HTML code before editing or adding code for the email.

If you would like assistance modifying the code, contact your account manager to discuss a billable service through our Professional Services team.

Additional Information
Email Formatting in Microsoft Outlook
Content in email displays differently when using different email clients