After rebooting the server we're seeing that the web interface isn't loading and I can't conect to MAPI.

The following events are being logged, multiple times.

Event code: 3005 Event message: An unhandled exception has occurred. Event time: 15/01/2020 00:17:03 Event time (UTC): 15/01/2020 00:17:03 Event ID: 8be19a0857444649b9b44cee7d588dd9 Event sequence: 5009 Event occurrence: 158 Event detail code: 0 Application information:    Application domain: /LM/W3SVC/2/ROOT-1-132235207043842752    Trust level: Full    Application Virtual Path: /    Application Path: C:\Program Files (x86)\SmarterTools\SmarterMail\MRS\    Machine name: MAIL-2 Process information:    Process ID: 3172    Process name: w3wp.exe    Account name: NT AUTHORITY\NETWORK SERVICE Exception information:    Exception type: PipeException    Exception message: The pipe endpoint 'net.pipe://localhost/SmarterMail.Interface.Authentication.IAuthenticationService' could not be found on your local machine. Request information:    Request URL: https://mail.domain.co.uk:443/Microsoft-Server-ActiveSync?Cmd=Ping&User=user@domain.com&DeviceId=SEC10C1F2F137A70&DeviceType=SamsungDevice    Request path: /Microsoft-Server-ActiveSync    User host address: 90.212.70.146    User:      Is authenticated: False    Authentication Type:      Thread account name: NT AUTHORITY\NETWORK SERVICE Thread information:    Thread ID: 21    Thread account name: NT AUTHORITY\NETWORK SERVICE    Is impersonating: False    Stack trace: Custom event details: 

Restarting IIS fixed the problem.