Connect to Outlook is missing in SharePoint Calendar

A very common & known issue while migrating IE versions. There is couple of steps and checking should be done to get this resolved.

• Make sure a single Office instance installed either 2003 or 2007 not both. In case you found a single instance of another version try below step.
• Manually unregister and register the owssupp.dll with regsvr32 , if this will not resolve your issue try below step.
• Enable add-on called “SharePoint Stssync Handler” in Internet Explorer. Go to Tools > Manage Add-Ons and look for add-ons called “SharePoint Stssync Handler” if disabled, Enable it. If enabled, disable it restart IE and re-enable it.  Still getting issue try below one.

• SharePoint Services Support feature should be installed on the machine.Control Panel > Microsoft Office > Change > Add or Remove features and add WSS features

For more on SharePoint STSSYNCHANDLER: Connect to Outlook to synchronize lists:

http://msdn2.microsoft.com/en-us/library/ms456225.aspx /   http://blogs.technet.com/b/josebda/archive/2007/03/26/searching-the-visible-moss-2007-code-for-activex-references.aspx