tangy_dandelion pop up

Hi,

Whenever I open up e-mail a "tangy_dandelion" tab appears, as if I have opened it from my e-mail.  However it's not in my inbox and was not sent from my account as stated.  I cannot get rid of it and I am reluctant to actually open it incase harm is caused.  Has anyone come across this, or does anyone have a solution for it's safe removal?

 

Many thanks