Regarding your contacts, if they were only in the auto complete folder and not actually saved in the contacts folder on BTYahoo then they would not have been carried over when your email account was migrated to the "new" BTMail.
When you are using the "Auto Complete" function you are not using the list of contacts stored in your Contacts folder.
In order to use the "Auto Complete" it must first be populated. Unfortunately your previous auto complete addresses were unable to be carried over when your email account was migrated from BTYahoo onto the "new" BTMail system. This means that you have to now re-populate the auto complete list.
You should make sure that in the settings, which can be found by clicking on your user name at the right hand side, you go to "Mail" then tick the box "Auto Save New Contacts" and then in click on "Contacts" in the list below "Mail" and tick the box "Enable Contacts Auto Complete"
This should then start to populate your auto complete list when you receive emails and reply to them.
