mail_read_tracker fails when celery is not installed

[kaleb]

Do you want to request a feature or report a bug? bug

What is the current behavior?

mail_read_tracker view raises exception if celery is not being used and is not installed

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

• Add dbmail.urls to project urls
• Attempt to go to /dbmail/mail_read_tracker/ENCRYPTION URL
• notice exception

Full traceback

ImportError for celery

What is the expected behavior?

Should be able to work without celery installed

Which versions of DbMail, Django and which Python / OS are affected by this issue? Did this work in previous versions of DbMail?

Not relevant