Mail Outgoing server Problem (Mojave)

Just upgraded to Mojave (iMac Late 2013 from 10.9) and now my iCloud account will not send any mail. I can switch to another SMTP (i.e. Google) and the mail will be send. But this is also changing my email address.

1) From the Outgoing Mail Server pulldown I can select iCloud (no change to sending)

2) I tried to Edit the SMTP Server list

as reported by others not all SMTP Servers are listed (iCloud is not)

creating a new one with iCloud specs (I leave the Server blank) does not change anything

3) Using the Connection Doctor - at times (not always) all Servers (IMAP and SMTP) are Green; but sometimes there is no connection to the iCloud SMTP (not even attempted); and sometimes iCloud SMTP is red

4) When selecting outgoing Servers in the pulldown menu (Preferences) - at times the selection can automatically reverted back to NONE - after about 3-5 seconds

5) I am also using my mobile MacBook Air and have no problems with any Mail sending (same accounts of course)

Q: Do I have to delete the iCloud account? Will this make a 'clean' install?

Thank you

Svend