Sporatic Mail Receive and/or Send

Greetings Robert, who is your eMail providers?

Make a New Location, Using network locations in Mac OS X ...

http://support.apple.com/kb/HT2712


System Preferences>Network, top of window>Locations>Edit Locations, little plus icon, give it a name.

System Preferences>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.

The interface that connects to the Internet should be dragged to the top of the list.


If using Wifi, instead of joining your Network from the list, click the WiFi icon at the top, and click join other network. Fill in everything as needed.

System Preferences>Network>choose interface>Advanced>Proxies Tab, make sure none are set, like for HTTP & HTTPS.

System Preferences>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...

8.8.8.8

8.8.4.4

1.1.1.1

9.9.9.9

Apply.

Great news Robert.:)

Sometimes we don't know the cause of the problem, just how to skirt the problem. ;)

To start off theNew Location replaces a dozen or so Internet related files that can get corrupted...easier than going one by one testing them.

Dragging to the top of the list, forces OSX to look for a connection on that interface first.

The Join other network sort of forces OSX to use the correct password.

DNS Servers are a bit like Phone books where you look up a name and it gives you the phone number, in our case, you put in apple.com and it comes back with 17.149.160.49 behind the scenes. :)  

These Servers have been patched to guard against DNS poisoning, and are faster/more reliable than most ISP's DNS Servers.

In a browser's URL bar, put this & hit enter, does that get you to Apple?

17.149.160.49

I believe the DNS additions also force a resetting of the DNS caches which can go stale, but have no real proof of that. :)