The SmarterMail Service just crashed for us.
Outlook wasn't opening on my laptop, so I rebooted. After rebooting and starting Outlook again I kept on receiving the credentials prompt, but my password wasn't accepted.
Turns out the SmarterMail Service had crashed - I doubt this had anything to do with the laptop reboot.
Here's the relevant event from the server log.
Faulting application name: MailService.exe, version: 100.0.7314.21902, time stamp: 0x5e18cc16 Faulting module name: ntdll.dll, version: 6.3.9600.19478, time stamp: 0x5d6aa558 Exception code: 0xc00000fd Fault offset: 0x0000000000030f56 Faulting process ID: 0x16fc Faulting application start time: 0x01d5c8d9cfd2906a Faulting application path: C:\Program Files (x86)\SmarterTools\SmarterMail\Service\MailService.exe Faulting module path: C:\Windows\SYSTEM32\ntdll.dll Report ID: c9a4b139-3726-11ea-80c6-54bf64fc2903 Faulting package full name: Faulting package-relative application ID: