iMac Mail Has Been Rendered Useless.

Open Keychain Access and search for your email account entries. You may have other entries that use your email address as a username, but those are not important, just the entry for the actual accounts.

Find all of them and delete them.

Then, try to set up your accounts again.

Please describe the "infernal loop."

Mail>Preferences>Accounts, but has been rendered mostly useless with the Auto setup eMail accounts.

Note, it would've been better to continue with the original post or at lest copy what did NOT work so every helper doesn't need to research what it was that didn't help. :)

To find out if it's system wide or user specific, try this...

Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.

Does it work in the new account?

What version of macOS are we talking about?

If your running an older macOS hence older mail, I suggest you try an other email client. I use Thunderbird. Running a third party email client means you can get the latest email standards.

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google is on a security binge.

You could have run into Google rating Apple Mail insecure.

Here is a google page about it.

Control access to less secure apps - G Suite Admin Help

Less secure apps & your Google Account - Google Account Help

You need to scroll down to less secure apps.

Your screenshots are probably being dropped because you are revealing your e-mail addresses.

How are you setting up your e-mail accounts, you need to do it through System Preferences> Internet Accounts

when the panel opens click on Add Other Account, then click on Mail Account, on the dropdown that appears give your account a name then fill out your e-mail address and then enter your password for that e-mail address.

I think you have enough memory.

My Dad's 2008 iMac got strange glitches like finder not display all files in a folder. I wrote it off as my Dad doing strange things until I saw finder not displaying all files in a folder. I bought an external harddrive. Re-install macOS and all third party apps from scratch Problem want away for awhile but came back. Just strange glitches with the finder. I convinced the parents to buy a new iMac.

I'd run etrecheck. Etrecheck will analyze your machine and software and report back. Experienced users have found the reported information useful when diagnosing problems. Post results here so others can view. The proprietary stuff in the report gets filtered. You may want to start a new thread. Include a link to this thread.

Install and run

-- Download etrecheck.  Goto the  EtreCheck  download page.  The download link is at the bottom of the screen

-- Install etrecheck. Goto your download folder. Double click on EtreCheckPro.zip

-- drag the app to the application folder if you wish.

-- Double click on etrecheck to run.   The first five runs are free.

• An alternative explanation how to install, run and report output for the EtreCheck Application
• Using EtreCheck to Troubleshoot Potential… - Apple Community
• -- Explanation of EtreCheck  output by etresoft, the author.
• Using EtreCheck - Apple Community

How to report etrecheck data.

When the report is done, click on the export icon.

click on "Copy report" to copy to the clipboard

Get back in your web browser and access your discussion. Create a new reply. Click on the <> code icon. Paste you etrecheck output into the code block.

which results in...

Robert
PS. You may find Old Toad's write up helpful.
How to use the Add Text Feature When Post… - Apple Community

Had you done a reboot. The old reboot is a cure for lots of evils.

R

Take multiple screen images to avoid showing any of your personal information or use preview to edit out your personal information.

I picked the box tool.

That is amazing. We do not recommend running that app. There are numerous report in these forums of problems caused by that app.

R

Next time we can suggest running safe mode. could suggest deleting and re-defining ethernet connections.

R

Arnel Nacino wrote:

Epilogue - None of the well-intended suggestions offered here solved my iMac Mail problems completely.

I ended up buying Cleanmymac 3. After installation, ALL my problems having to do with iMac Mail are gone.

You'll be back with a whole new set of problems. Uninstall CMM.