Mail Queue is not sending mail

Hi Atlassian,

We have recently upgrading our environment from XEN to VMWare. This went very smoothly by performing an rsync to create a exact replica of our previous instance. When testing the Mail Server everything went well when using the "Send Test Email" option however this appears to bypass the Mail Queue providing us with a false positive. Currently email notifications do not work for anyone as the Mail Queue is processing however the emails do not successfully reach the recipient.

We have confirmed this is not an issue caused by our Mail Server as our previous environment does not have this issue using identical settings. After enabling DEBUG mail logging for com.atlassian.confluence.mail we noticed some worrying log entries such as

2015-03-30 12:33:00,026 INFO [scheduler_Worker-7] [confluence.mail.template.AbstractMailNotificationQueueItem] send Not sending email because sending is disabled via system property.

I assume this system property is my problem. If so how do I enable sending? What could have caused the disabling of sending?

Is this System property we are looking to change atlassian.mail.senddisabled?

P.S We are running on Red Hat Linux 6.5