There are a few reasons why this may occur:
  1. If you copied an appeal mailing, the mail date copies from the original mailing.  In this case, your mail date may be a past date.  Go to Marketing and Communications > Appeal Mailings.  Click on your mailing, click Edit Mailing under tasks and edit the date.
  2. The mail date field is manually entered so if you entered a different date than when you sent the email or scheduled the email to send, the mail date and email job date would be different.