Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Wow! A sure way to get into a bit of trouble!

Thankfully for me, it's not that big an issue. But I am concerned about my.mac option being greyed out.
I believe it's grayed out because it's your Apple ID. I think that's a good security measure.
 
Well, oddly enough, even though my .mac option remains greyed out, I sent an email just now to my gmail and it is again showing as being sent from .mac. Must've been a glitch.
Do you you see other aliases set to ON? I had to make all the aliases to OFF to make it work, except @Mac that is grayed out.
 
Hey Guys,

So I think I found a solution that seems to work. I upgraded tokay to iOS 14.0.1, thinking that they would have fixed the issue, but the test email I sent continued to come from @icloud.com. Then when I went to the Mail settings, I noticed that all the other aliases had the Allow Sending From as ON. The description of the option reads the following:

"Choose which addresses you would like to use when sending from your iCloud account. You will still receive mail at all of the addresses above."

That led me to go and toggle all aliases [non @mac.com] to OFF. That did the trick! The emails are sent from @mac.com and based on the description above, and you will still get emails for the other aliases. I hope this helps.

iOS 14.2 beta hasn't solved the problem for me. And I can't for the life of me find where this setting/message occur in Mail or iCloud settings. All I see is a "Reachable at" section, but that won't allow me to turn off the iCloud.com or me.com versions.
 
I just found out that the fix I had shared earlier doesn't seem to be working consistently. I went back to the check on the settings for the Mail app. For some reason, all the aliases were back to ON, causing the email to sent using @icloud.com again. I had to go back and turn all the non @mac.com email aliases OFF. Make sure you press DONE after that, pressing CANCEL or tapping outside the window puts everything back to ON; even if go back to make sure the settings took effect! Bizarre bug. I added a screenshot of the screen I am referencing below.

45AD58C6-EC66-477A-B8C0-9117887AC351.jpeg
 
The only system that works consistently is to send the email from iCloud.com. I don‘t like the browser based UI, but that seems to the option until Apple fixes this problem.
 
It looks like Apple finally is acknowledging it. Hopefully the update will fix it.

iPadOS 14.1 includes improvements and bug fixes for your iPad.
  • Fixes an issue where some emails in Mail were sent from an incorrect alias
Some features may not be available for all regions or on all Apple devices. For information on the security content of Apple software updates, please visit this website: https://support.apple.com/kb/HT201222
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.