Mine have not changed, so I think you might need to look at another source. Perhaps some sort of "system tune-up" software or space saving one. Most utility software that says it can fix complex issues like speed actually does more hard than good.

Thank you for responding.

I've never used system tune-up or space saving software or other "fix it" software other than letting Windows try to diagnose a network error.

Can the server somehow trigger any settings in the email client?

On further inspection, only the POP accounts from one particular email plan had the issue.

which mail provider is it?

There are al lot of settings here https://autoconfig.thunderbird.net/v1.1/

These are what Thunderbird reaches out to get when you create a new account. But I am not aware of any with retention settings, on basic settings like port and server name really.

Other things to look at are addons and anti virus. They sometimes meddle where they do not belong.

GoDaddy. Their workforce email, not their Microsoft Office 365 email.

That link appears as a directory to me.

I did create a new account in Thunderbird a couple months ago, and I left it in even though I deleted the email account on GoDaddy.

I will check anti-virus. I did try out a couple different ones lately.

Thank you again,