Have you considered that Microsoft and Apple are two of the largest providers of email services on the planet and that maybe those are working correctly and your ISP is the one causing you problems? Not being able to send mail is often caused by mail providers that are still using insecure protocols that should have been retired decades ago.
I would recommend removing all account settings from Mail and then starting fresh one account at a time. If you add a single iCloud accout to Mail, does it work? If you then add a Microsoft-hosted account does that work? I am guessing that the answer is that they both work just fine.
Then, if you add your ISP-provided email account, do you start having provlems? If so, the problem is with your ISP. Email acocunts provided by ISPs are some of the most unreliable and problematic email accounts of all.
I would highly recommend establishing an iCloud email account and migrating all of your email to it over time and abandoning your ISP-provided account.