Email Tracking/Set Regarding from Outlook Not Showing in CRM

Hi all,

When I send an email and select 'track' or 'set regarding' and select, for example, a specific account or contact, the email activity does not appear in CRM.

I've followed the instructions on this link: http://www.summitgroupsoftware.com/blog/unable-see-crm-outlook-client-tracked-emails-regarding-records and ensured all my settings are correct, however the below may highlight the root of the issue

The incoming email/outgoing email and appointments etc are all showing as failure and the mailbox is disabled for email processing.

I feel like i may have missed a step somewhere, any ideas on what they likely causes of this failure may be?