Can't Sent E-mail on iCloud Account from Apple Mail
I'm at my wit's end trying to solve this problem. I've been trying to work with Apple Support on this issue since mid-July and keep getting bounced around in their system and have yet to get any help in resolving it.
I am using a 15-inch 2018 MacBook Pro with 32 GB of RAM and a 1 TB SSD drive running macOS 11.6 (latest version). I use Apple Mail with a combination of e-mail accounts, including Gmail, 3rd party e-mail, Microsoft Exchange, and iCloud.
I sent the computer off to have its battery replaced back in June (and Apple also swapped out a problematic butterfly keyboard at the same time). While it was gone for service, I used a replacement MacBook Pro that I logged into my iCloud account to keep things synced for me while I worked on the loaner machine. When I got my computer back, I signed out of my iCloud account on the loaner Mac and erased its hard drive, taking it back to its factory settings. I then logged my MacBook Pro back into iCloud and the problems started.
I logged back into my iCloud account and everything worked except sending mail from my iCloud account in Apple Mail (I receive iCloud e-mail with no problems). If I try to send any e-mail from my iCloud account in Apple Mail (no matter the e-mail size or whether is does or does not have attachments) the mail sits trying to send for about 10 minutes, then errors out, saying that it cannot reach the SMTP server and asking me to choose a different e-mail SMTP server. This happens no matter the network my MacBook Pro is connected to (either wirelessly or by ethernet). My iCloud account works perfectly fine through the web browser on my Mac and on both my iPhone and iPad.
Apple Support had me delete and add back the iCloud SMTP server (no fix), re-install macOS (no change) and then did videos and screenshots of my Apple Mail program to send to their engineering team. In amongst all this, I kept getting handed off between Apple Support team members who repeated each of these actions several times to no avail. Finally, they had me make sure I had the latest version of Big Sur installed (which I did) and try to send again (and it still will not send mail from my iCloud account).
Connection Doctor shows that the SMTP server for iCloud never completes its connection and therefore does not work (it just shows the spinning circle).
I have some other SMTP servers that show they do not connect (but they do not stall out like the iCloud connection).
Does anyone have ideas on how I can fix this? I have written Apple Support twice in the last week to re-open the case and they have not replied. I need to get my iCloud mail fixed so I can send from it on the Mac.