Assuming you mean an iCloud email account:
Settings>iCloud>Delete Account (only deletes it from this device, not from iCloud;
To delete from iCloud and your device, turn off all iCloud functions for the account in Settings>iCloud, then delete the account as above.)
How to Delete Gmail Account on iPhone (2021)
Deleting your Gmail account from your iPhone is a pretty straightforward process. Here’s how to do it:
1. Open the Settings app on your iPhone.
2. Scroll down and tap on Accounts & Passwords.
3. Tap on the Gmail account that you want to delete.
4. Tap on the Delete Account button.
5. Confirm that you want to delete the account by tapping on the Delete Account button again.
And that’s it! Your Gmail account will now be deleted from your iPhone.
Frequently Asked Questions with answer of How do I delete an old email account from my iPhone?
To delete an inactive email account from your iPhone, go to Settings > Accounts & Passwords > Delete Account.
There isn’t a way to make your iPhone forget old email addresses, but you can delete them from your Contacts app.
There is no one definitive answer to this question. Depending on the email service, you may need to unsubscribe from all mailing lists, delete the account, or contact customer support.
Go to Settings > iCloud. TapDelete Account. (This will delete the account from your iPhone, but won’t affect your iCloud data.)
There are a few possible reasons why you may not be able to delete mail on your iPhone. One possibility is that you do not have the correct permissions set up on your device. Another possibility is that there is a problem with the mail server that you are using. Finally, it is also possible that the mail application on your iPhone is not working correctly.
Conclusion
There is no one definitive answer to this question. You may need to contact your email provider for specific instructions, or you may be able to delete the account directly from your iPhone’s settings.