SMTP Mail Issue : cant send e-mail from any account (including my Icloud mail-address) while Connection Doctor is showing ALL GREEN. (Incoming mails do arrive)

Similar issue as: Cant send e-mail with the server iCloud - Apple Community

But posting again as it's closed without a solution!

Suddenly not a single of the 'larger' smtp servers (apple, google, ...) is working anymore on my macbook pro. When browsing to icloud.com or sending mails with any other device is okay and working correctly. I also tried to add Icloud smtp and google smtp and those worked for 1 time and then again errors like we see in the other articles.

The stranger thing is, the apple mail Connection Doctor is showing GREEN for ALL smtp's, so why aren't the mails send? This seems to be an issue in apple OS or app, otherwise it should show red, no?

I didn't change anything in my mail settings and while ALL smtp's are failing is leading me to think there is a general issue with apple and not with the single smtp servers. Why would all different smtp fail at the same moment?

The last answer in the link above was from 2019:

"Based on the issue and the isolation steps you've tried so far, it sounds like an issue that will need to be investigated further by Apple." --> Why didn't they investigate and share the outcomes? Somehow disappointing that there is no answer from Apple on the investigation and seen the many articles about the +/- same issue I think many people suffer from this.

Apple mail is already too basic to be candid.

It's surprises me to see friends are using Google mail on their macbook because apple mail is too limited in functionality. It's even impossible for me to resize the image of an email signature or add a specific font in apple mail.

And so the second question is: why is apple mail so basic that it looks to come from the early 2000's. Even creating an (apple !!!) calendar event directly from the (apple !!!) mail is not possible. What?! Why?!

Did apple fall asleep doing continuous improvement with apple mail?

Please correct me if my knowledge about the functionalities of apple mail are not up to date but in my opinion apple mail is not delivering the quality you expect (and pay !!!) from the apple company.