Incident Resolved
The works to replace the main firewall cluster have been completed successfully, logins have been enabled for all platforms.
Update Number: 20 (Entanet / Cityfibre)
14:31 (Customer impact resolved post card Swap out at 19:25 on Saturday 23rd July)
This has now been resolved.
Mimecast report that their system is back to normal and all email backlogs have been cleared.