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If the address that's being selected is an account you no longer wish to use on your iPhone, it can be removed or you can choose to temporarily stop using it with the following steps:
Temporarily stop using an email account
If you want to temporarily stop sending and receiving email from an account on your iPhone, you can turn it off in Settings. You can easily turn it back on at any time.
1. Go to Settings 
> Mail > Accounts.
2. Tap the email account you want to turn off, then do one of the following:
* Turn off an iCloud email account: Tap iCloud, tap iCloud Mail, then turn off Use on this iPhone.
* Turn off another email account: Turn off Mail.
Tip: You can choose if you want to continue using other apps with this account—including Contacts, Calendars, and Reminders. Turn each individual app on or off.
Delete an email account
You can remove an email account from the Mail app 
and from all the apps that use it on your iPhone.
Note: This action doesn’t cancel the email account; it just removes it from your iPhone. To close the account completely, visit your email account provider.
1. Go to Settings > Mail > Accounts.
2. Tap the email account you want to remove from your iPhone, then tap Sign Out or Delete Account.
3. Note: If you change your mind later, you can add the email account back to your iPhone. See Add an email account.
Add and remove email accounts on iPhone
Messages can be moved from a mailbox to another, using the steps found here:
Organize email in mailboxes on iPhone.
If there are additional options or features you'd like to see, we recommend providing feedback for Apple: Apple - Product Feedback
Cheers!
