Mac Outlook Express 5.x Error -16999

This error can occur on all versions of Mac Outlook Express 5.  Reasons why you may encounter this error are as follows...

1)  "Always use secure password" is ticked in the advanced receiving options

• Go to Tools > Accounts

• Double-click the Account Name or highlight it and click Edit.

• Click the Click here for advanced receiving options button.
• This should pop up the panel shown below.
• Make sure that Always use secure password is NOT ticked.
• Try to receive mail again.

2)  Outlook Express trying to download when there are no messages on server

Very simply, there is a known bug in Outlook Express whereby it can display the error when attempting to download mail from an empty mailbox.

3)  Mail server blockage

There may be a blockage on the mail server stopping any mail from being downloaded.

4)  Outlook Express 5.01 needs to be upgraded

Outlook Express 5.06 is the newest version of Outlook Express available for the Mac.  It doesn't suffer from problem (2) - in other words, it should never report an error if the mailbox is empty when you try to download mail.  To check which version of Outlook Express is in use, do the following... 

• With Outlook Express open, go to Apple > About Outlook Express...
• The Version is listed in the middle-right of the splash screen below.  

NOTE: If none of the above processes resolve this error message, do the following...

1.  Compact the Outlook Express Database (relaunch Outlook Express whilst holding down Alt on the keyboard, then click Yes to the prompt that is displayed.)  Try to retrieve mail again.
2. If this fails, quit Outlook Express and launch the Microsoft Internet First Run application. This application's function is to restore any missing Internet Explorer and Outlook Express components.  If the Customer does not know where the Microsoft Internet First Run application is stored, carry out a search for the words First Run and launch the application directly through the search results pane.  Relaunch Outlook Express and try to retrieve mail again.
3. If this fails, create a new Outlook Express Identity and try to receive mail again.
4. If this fails, Outlook Express may need to be completely reinstalled.

NOTE: This error can sometimes occur if one of the e-mails waiting to be downloaded has a very long subject line (greater than 128 characters).