Apple Mail - outgoing SSL server issues

After hours of tech support calls and feverish googling, this seems to be my last hope, my Obi-Wan if you will. Each year, my ISP (Newtek Webhosting) makes a change to their system and/or Apple makes a change to its server/email protocols that causes my Apple Mail to fail, and as a business owner of 25 years, I am stuck without email for days, sometimes weeks. Eventually we find the solution. But during that time, the ISP throws Apple under the bus and Apple throws the ISP under the bus, and nothing gets solved. That is what is happening again, only it's been 8 days without email.

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Here's the issue: my ISP last Thursday changed a configuration related to the SSL servers that caused Mac Mail to not be able to pull down my emails to my OS (only) devices. I can still get email on my iOS devices. When we tried to uncheck SSL and change the port from 995 to 110 and save it, Apple Mail returns a "Invalid user or password" error, which is not accurate. The user and password are 100% for certain correctly entered. We have verified this many times.

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What the ISP and I -think- the issue is, is that there is no way to basically 'reset the cache' on what Apple Mail thinks is the port # and other settings to retrieve my emails, and since we cannot save the 110 port setting (which should work), we can't solve the issue. The ISP says 'Your mail is getting to our smartermail app so our service is working fine, it's Apple's problem." Apple Senior Tech Adviser does all the annoying reflective listening and pseudo "I understand your frustration" nonsense that does zero good, (and in fact only causes more frustration) and then blames the ISP.

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Has anyone had a similar issue with this "Invalid user and password" false error when trying to update outgoing email server settings during a somewhat similar problem? Any websites, forums, articles, experience that might help me get my email back?

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Thank you for any attempts to help. It's more than Apple or my ISP have done.