The actual text says something about a "strange networking error". The reason for this problem is simple: Open Transport preferences are corrupted. They need to be deleted and the TCP prefs reset. Here is a link:
And a text only version:
Error -3279: Mail could not be received at this time. A network error has occurred.
1. Double-click the Macintosh HD icon.
2. Double-click the System folder.
3. Click and hold the MacTCP DNR item in the folder, then drag it and release it on the trash can.
4. Double-click the Preferences folder.
5. Click and hold the TCP/IP Preferences item in the folder, then drag it and release it on the trash can.
6. Close all windows.
7. From the Special menu, choose Restart.