I usually only use one BT email address but recently set up another. How do you quickly toggle between the two accounts ?
Assuming that you are the "owner" of both email accounts you can access them both by logging onto the one you deem to be your "Main" email account.
To do that you need to log onto your main email account then go to the Settings which are found by clicking on your user name at the top right.
Once there go to "Mail" > "Accounts" and then click on "Add". When the new box opens enter all the relevant details and click save.
You will then find the "added" email account below your list of folders on the left hand side of your "Main" email account.
If you click on the account name it will open the account and its folders. To go back to your "Main" account click on "My Account" .
As well as entering the new email address, password and selecting IMAP in the drop down for account type, you will need to go to advanced settings and enter mail.btinternet.com for both incoming and outgoing server, enter port993 and tick SSL for incoming and enter 465 and tick SSL for outgoing.
However, the simplest way to deal with multiple email addresses is to use the right tool for the job, a mail client such as the free Thunderbird. All your inboxes are then in one place and you don't have to switch between accounts.