|re: "The only way that I can think of is by using the Calendar function of Outlook"|
There may be ways to do this within Excel itself, but we need some more info.
Dates can be checked upon the opening of the workbook and emails sent, etc. It might be tricky to do without opening the workbook (or at least some workbook) so that some action occurs to cause the date to be checked.
The workbook can't just be sitting in a folder checking itself.
In any case, VBA would ceratinly need to be involved.