Test the Appearance of Marketing Cloud Emails

Partnership with Return Path

Through this partnership, there are options for several reports that can be accessed through the Marketing Cloud application:

Inbox Preview
Inbox Detective
Reputation Monitor

Specifically, the Inbox Preview report can help you to preview what an email message will look like when opened in different email clients prior to sending. 
 

Test Accounts

Another option is to set up test subscriber records that are associated with all of the major email clients. Focus on the major ESPs or more specific ones as needed based upon your audience.  Examples of major email service providers include Gmail, Hotmail, AOL, Yahoo, and Outlook. Remember that there are newer and older versions of most email clients and thus rendering may differ between said version.  If appropriate, you may also find it necessary to test each ESP in the major web browsers. You can then use the Marketing Cloud Test Email feature to preview email formatting.

Tip: Gmail will expose syntax errors. Additionally, Outlook 2007 and Hotmail in Firefox tend to expose major rendering problems. It's important to test in all email clients, but these are especially key.