NO_MASS_MAIL_PERMISSION, Single email is not enabled for your organization or profile issue in salesforce

This issue will generally come from spring13 release, when you refreshed a full sandbox and trying to send e-mails via Apex this may lead you to an issue saying that
"NO_MASS_MAIL_PERMISSION, Single email is not enabled for your organization or profile. Single email must be enabled for you to use this feature". 

To get rid of this issue 

go to Administer > Email Administration > Deliverability and then you will have options to select like No access,System email only, All email. select All email from the list. 



• No access: Prevents all outbound email to and from users.

• System email only: Allows only automatically generated emails, such as new user and password reset emails.

• All email: Allows all types of outbound email. Default for new, non-sandbox organizations.