By some reason if the email are not sent even though Email campaign is scheduled, you can follow the instruction below to rectify the issue.

Click on setup→  Schedule Jobs→ 

Please make sure that you can delete below MassMailer related schedule Jobs.

1. Campaign Scheduler H

2.  Mass Email Ststistics Reporting

3.  Campaign Scheduler M

4.  Mass Email Wizard H

5.  Mass Email Wizard M

6.  MassEmail Scheduler Point2Point H

7.  MassEmail Scheduler Point2Point M

8.  Bronze User Scheduler

9.  Campaign Aggrigate Email History

Once these scheduled jobs have been deleted then you can go ahead and activate the scheduled jobs again by following the instructions below.

Click on Mass Mailer Setup---->Schedule then hit Schedule button.