If they are not in any of the folders in your email account it means that they are not there. You would need to get the sender to resend them to you but before doing that add the senders email address to your "Safe Senders" list.
Log onto your BTMail account using a browser, not an email client/app, and then click on your username at the right hand side. Select "Settings" then go to the left hand side and select "Mail". Scroll down and click on "Safe Senders" and add the sender's email address then click "Save".
You should also check your "Blocked Senders" list for the email addresses and also for the email senders domain name, that is the part after @.
Once you have logged onto your BTMail account and clicked on your username at the right hand side. Select "Settings" then go to the left hand side and select "Mail". Scroll down and click on "Blocked Senders". Scroll down the list until you find the email address and domain name that you want to unblock and select it. Click on "delete".
