Yahoo Not Connecting With Apple Mail - MacBook Air

Yahoo mail is now failing to display emails in Apple Mail on my MacBook Air. I have deleted the Yahoo from the normal mail preferences then re-installed. but still no joy.

The Apple Mail advises "Connecting" eventually, with no emails being displayed (either sent or received).

The Apple Mail 'In box' displays a warning/alert ! symbol. On selecting, the Apple Mail warning message is displayed advising:

ONLINE STATUS

Connections to the server"imap.mail.yahoo.com."on the default ports timed out.

Does anyone have any ideas on what is happening or whether I need to make adjustments to the 'Proxy' Settings? i.e. select the correct protocol to configure in System Preferences>Network>Proxies

Currently only 'SOCKS Proxy' is ticked as well as "Use passive FTP Mode (PASV)" is also ticked.

FYI it works fine on my iPhone