macmacosnotes.app
I got a new Macbook yesterday, so I was trying to configure an email account.
At the same time, I recorded some important notes in the "Notes", which were automatically bound to this email account by the system. (which I was not aware of )
This morning, I just found that the email account was not configured correctly, so I deleted it and re-configured a new account.
Then I found that all the notes I recorded yesterday are gone.
Is there any method to recover these notes?
Syncing the notes to your computer, then moving the notes to your email notes and letting it sync back to the phone would be the easiest.
Without syncing you could email each note to yourself by clicking the envelope icon at the bottom of each note. Then turn it into a note in your email account, of course this would take a long time but you wouldn't have to sync with your computer.
If I'm reading the initial question correctly, you wish to select which account new mail comes from.
In Mail prefs > Accounts > Account Information tab you can enter multiple email addresses in the Email Address field. You must separate them by commas.
When you create a new message The From dropdown will list every email address. These addresses will be used in the From: field.
Best Answer
If your notes are really stored in your email account, you should be able to reconnect to the same email account over IMAP to gain access to your notes again. Do not configure the email account as POP3 for example.
However, if you really have a new MacBook, it is probably running El Capitan. With El Capitan notes are no longer stored on IMAP email accounts - in fact it is not supported at all. Most likely your notes are really stored in iCloud, and you need to relogin to iCloud or reenable Notes in the iCloud preferences to access them.