Re: "Deleting me.com email address ..."
Apple support have an article online (link below) the may be helpful:
About your @icloud.com, @me.com, and @mac.com email addresses - Apple Support
Eg: says:
"Depending on when you created your iCloud account, your iCloud email addresses and aliases may end with @icloud.com, @me.com, or @mac.com domains".
and
:If you created one or more email aliases for your account, remember:
You can change or delete an email alias, but if you delete an @mac.com or @me.com email alias, you can't add it back to your iCloud account."
Then: Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support
Eg: says:
"Turn off, turn on or delete an alias"
"You can turn an email alias off or on at any time.
You can also delete email aliases that you no longer want to use.
Turning off an email alias is temporary; deleting it is permanent. When an alias is turned off or deleted, emails sent to that alias are returned to the sender.
Go to icloud.com/mail, then sign in to your Apple Account (if necessary).
Select (the circular cogwheel with three arms icon) at the top of the Mailboxes list, then choose Settings.
In Account settings, select an iCloud Mail alias in the list, then do any of the following:
Turn off an alias: Select the “Disable alias” checkbox, then select Save Changes.
Turn on an alias: Deselect the “Disable alias” checkbox, then select Save Changes.
Delete an alias: Select “Delete alias”, then select Delete.
Note: If you have three email aliases and you delete one, you must wait 7 days before you can create a new one."
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Re: ".. and fixing default From email address (when sharing in other apps)"
Try Settings > Apps > Mail > scroll right down to "Composing" > Choose which default account you want to appear.
(ie: Messages created outside of Mail will be sent from this account by default)
