Hello Lakshan, and thanks for your post here. First, the hostname field on domains is expected, or at least is something we have seen previously. The hostname field used here wasn't present in the previous versions, so this is not set on upgrade. We have plans to default this to mail.domain-name.com in the future so it needs even less configuration!
On the calendar issues, this sounds like the user's original XML configuration files were not successfully converted to JSON format, and likely need a re-convert. Can I have you submit a ticket on this so we can take a look please? Hang on to your pre-upgrade backups for the moment as we can use these to reconvert the account as well. Thanks in advance!
Kyle Kerst
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com