Q: Why does Mail keep looping at "Select the apps you want to use with this account"?

Hello,

When I try to add a new "Other Mail Account..." email account to Mail, the application gets stuck in a loop when I get to the page that says "Select the apps you want to use with this account." When I click "Done" on this window, the button then becomes "Next," and clicking that just briefly flashes a spinning gray wheel in the window but nothing happens. No matter how many times I click "Next" it won't finalize the account and this window stays open. Clicking Cancel will immediately quit Mail. I have tried combinations of selecting "Mail" and "Notes" in the list of apps, but this doesn't make a difference. I've also tried to create the account through Internet Accounts in System Preferences, but the same exact thing happens there too. I've tried restarting, deleting preference files, Application Support, all that stuff, but still no luck.

This is happening on Open Directory network accounts, running OSX El Cap 10.11.6. Version of Mail is 9.3 (3124)

The particular system from this example is a 21.5-inch iMac, Late 2009  3.06 GHz Core 2 Duo Processor, 4 GB 1067 MHz DDR3 RAM. Any help would be greatly appreciated! Thank you!