You might decide to try using a symbol or emoji in your mailing's subject line to call attention to your message. We've seen some cases of increased open rates for mailings using these, though it differs based on industry.
We tested using an emoji from Facebook Symbols across email clients. We copied the emoji and pasted it into the subject line field:
We found that the emoji didn't appear properly in Outlook 2003, 2007, 2010 and 2013's notification popups. Here's an example from Outlook 2010:
It also didn't appear properly in:
When it appeared as an error, it looked like a small box, a different pizza emoji (in color or black and white), two question marks or other decidedly non-original pizza emoji.
Here's how it looked in Android 4.0:
However, the emoji's appearance seems to depend on that character. Here, we tried two other emoji, also from Facebook Symbols. Here's how it looked in Mac Mail 7.2:
The bottom line: While not necessary to use, emojis can make your email stand out in an overwhelmed inbox, and we all know that challenge. We suggest split testing two or three subject lines to judge for yourself how your own contacts choose to interact with your mailings. And, as always, test, test, test before sending out to your audience.