Certain printers will always complain when the paper size is set incorrectly. Most applications will honour the printer settings defined on the printer driver, but some, like Outlook, need a little persuasion.
Open Microsoft Office Outlook
Click on: File -> Page Setup -> Define Print Styles
Highlight Table Style, then click on Edit
On the Paper tab, select A4 from the list of available Paper Types.
Repeat for Memo Style
This will show you how to build a new Identity in Outlook. On a Windows machine this would be call a new Profile.
Here is the Microsoft article on the subject (look for step 5): http://support.microsoft.com/kb/2360509
Kill all Microsoft Office applications processes (i.e. close them all, including Word, etc).
Press the Option (Alt) key while clicking on Outlook to open it.
It will go into the Microsoft Database Utility mode where you can rebuild the Identity (Database).
Click the plus [+] sign on the bottom left.
Name your new identity.
Select your new identity and click on the configuration icon config icon
Choose Set as Default
Close this window and open up Outlook.
Configure your exchange email account as you would for a new account
Note: for large mailboxes (multiple GB's), this may take a long time to complete