Airport Express Network blocks Mail server access

Question

Running 10.3.9. Mail version 1.3.11.
Hello
With my current network setup Mail is unable to download/send messages with my POP e-mail server. If I plug my laptop directly into the network cable (coming from our Linksys router), Mail can access the server.
My network setup is a Linksys 4-port router, wired to an Airport Express, that relays signals to 2 other Airport Express'. All other internet access/sharing works fine.
What Airport settings can I look at to fix the problem?
Thanks
Matt

Answer 1

Try the following on your Mac mini, in order, until (hopefully) resolved:
1a. Delete Preferred Network(s)
System Preferences > Network > AirPort > Advanced > AirPort tab
Under "Preferred Networks," delete the network(s) you regularly use from the list.
1b. Delete AirPort Keychain Entries
Launch the "Keychain Access" application located in Applications/Utilties.
Click on the "Kind" filter at the top, and look for any "AirPort network password" entries...and delete them.
1c. Add Preferred Network(s)
System Preferences > Network > AirPort > Advanced > AirPort tab
Add the preferred network(s) using the "+" button.
Restart or log out then back in.
2. Move System Configuration Files
(Note: You will have to reestablish your network connections settings.)
Go to /Library/Preferences
Move the SystemConfiguration folder to the desktop.
Restart your Mac. (Note: OS X will rebuild the files that are now sitting on your desktop. If this doesn't resolve the issue, you can move the folder back to it's original location.)