You have not said which email system you are on.
When you access your email on your computer is it via a web browser? Have you changed your password of your email account anytime?
If you are able to receive emails it is unlikely to be a password issue especially if you have not changed it at anytime but it is worth checking.
If you are using the standard email app on your Samsung J5 you should check that the settings are as follows:
Account Name: Your email address
Your Name: Self explanatory
Always Cc/Bcc myself: Your Choice
Signature: Your choice
Show images: Your Choice.
Skip to the advance settings and tap on Server Settings:
Email Address: Your BT email address
Password: Your email password.
Incoming Server:
Depending on which type of account you have set up you eill need to have the IMAP or POP3 settings as per this link
http://bt.custhelp.com/app/answers/detail/a_id/44917/kw/bt%20mail/c/6591
Out going server: Settings as per the above link.
Authentication required before sending emails: Make sure the switch is set to be on.
Username: Your email address
Password: Your email password. Ensure that it is correct and the same as the one you have used on your computer.
If your account still does not send emails you could try setting up another email app in order to test it. I use the AquaMail app. There is a free and paid for version. Just use the free version for the test.
