Ensuring 7 bit encoding

I hope that this question has a trivial answer, but that people won't
mind me asking it here. I've been googling the subject, but can't
quite get a handle on it.

What do I need to do to ensure that emails are generated only in 7,
not 8-bit encodings?  I assume that I need to use
email.charset.add_charset , but can't quite work out what incantation
to give it.  Does anyone have any pointers?

Best wishes,

Nicholas