ServiceDesk Plus  9.3 Build  9308 on Windows 2012 R2

External MSSQL Database

Exchange 2013 Version 15.0 ‎(Build 913.22)‎

Same network (no firewall)

Can telnet to all ports without issues

Can send mail via telnet (but sending is not the issue)

System Log Message: Exception while trying to open folder.

Probable Cause: A3 NO Server Unavailable. 15

now new errors appeared:

almost

We can connect via Outlook without issues. Checked for duplicate or problematic folders. Changed to POPs. Stoped and Restarted services and servers. 

On the Exchange side, everything seems fine. Mails are received and can be read via Outlook. SDplus can send emails when cases are opened from the portal. But seems not able to open cases from mails received.

Any help is greatly appreciated.

Thanks