Send email alert from escalation not generating email

I am trying to configure my user input task in such a way that if a task is pending for more than 90 days i am sending an email to a group of users that their task will be deleted

 

i am saving the corresponding group email id say for example " marketing_team@company.com" into an email constant and providing the constant in the recipient text box.

 

somehow the mail is not getting generated . i tried selecting a different user from the directory just for checking , no luck . can you please throw some ideas ?

 

  Discussion posts and replies are publicly visible