We have Accounts Payable version 8.1C (110729) and EFT version 8.1C (100811)
We are trying to e-mail advices to customers using EFT, however, the e-mail form is not turned on. How do we turn this feature on.

Under banks, disable the option to "Bypass additional forms?".

(If that's what you're asking. Otherwise, perhaps you could clarify "e-mail form is not turned on.")

Ensure you have 'Allow email' enabled for the user on User Preferences. Without this, email functions are hidden. A quick way to check is whether you see 'Email' as part of the Menu structure, to the right of Reports. If not, then email is not enabled for this user.

Then Andrew's advice will allow you to see the Additional Forms screen when printing/EFTing checks and see the email button there.

A short training video on Processing EFT demonstrates both of these points.