You need to give more details if you are looking for help.
Which email system are you on, is it BTMail or BTYahoo?
How are you using your email account, is it on a mobile device or a computer?
Are you using webmail (logging on via browser) or are you using an email client or app.
If you are using an email client or app, which one?
What setting are you using? the correct ones are as per this link
https://www.bt.com/help/email/manage-email-account/manual-settings/what-are-the-settings-for-outgoin...
Have you changed your password or deleted and re-set up the account on your device recently?
