Emoji's can definitely be inserted in to your subject lines and email body content, they are a great way to differentiate your emails from others and draw attention to the subject line or particular sections of your email.

Please be aware that although most modern email clients and web browsers support emoji's, some legacy email clients may not fully support these emoji's and will simply display an empty square box in place of the emoji.

Here us a full list of supported and unsupported email clients:

Email Client	Emoji's display in subject line and body content?
iPhone / iPad (iOS Mail)
Android Mail
Windows Mail
Gmail
Yahoo! Mail
Outlook.com / Office 365	Depending on computer font Emoji support
Inbox by Google
Outlook 2003	Not Supported
Outlook 2007
Outlook 2010
Outlook 2013
Outlook 2016

To see a full reference of Emoji's, please see our Full Emoji Reference.