I've been keeping part of an eyeball on potential Exchange replacements for some time. I gather that nothing matches the capabilities of Outlook+Exchange, it's one of MS's crown jewels in the enterprise space.

SME Server apparently comes with QMail: http://wiki.contribs.org/SME_Server:About#Platform_Specifics

Googling shows some people are trying to install Zimbra on SME Server.

For lurkers there is some overview information at http://www.outlookipedia.com/outlook/share-outlook-calendar.aspx .

Some more resources apparently reviewed June 9, 2013: http://www.slipstick.com/outlook/sharing/sharing-outlook-calendar-and-contacts/

Hosted Exchange is becoming more competitive for small business, for those cases where the cloud is an option.

>Hi,
> Has anyone come across something that will handled Outlook shared Calendars with SME?
>
>>>http://en.community.dell.com/dell-blogs/software/b/software/archive/2013/07/10/windows-small-business-server-discontinued.aspx
>>>http://www.theregister.co.uk/2013/07/11/death_of_microsoft_small_business_server/
>>>
>>>What now, SMEs?
>>
>>I'm trying to get up enough nerve to install SME and see if I can use it instead of SBS.
>>
>>Thats the Linux SME Server - http://wiki.contribs.org/Main_Page