Connections to the server “imap.gmail.com” on the default ports timed out.

HELP!! This has just recently started and although I am connected to the internet, all of my email accounts say the same, including iCloud. I can't seem to send out or receive anything. I spent hours this morning with an outside expert trying to fix this on my computer and he couldn't help. Is this a problem with my own internet server? No problem with my iPhone or iPad, just on the Mac.