EMAIL on MAC
Connection to server on the default ports times out on my MAC but works on iPhone and iPad. Happens to Gmail and Comcast IMAP accounts after upgrading to macOS High Sierra Version 10.13.6
iMac 21.5", macOS 10.13
Question marked as
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.