emails : dkim and multipart ?

hi there ! hope i'll find solutions here...
I'm looking for two many things with automatic emails (email confirmation, approval...)

1/ how to sign the messages with DKIM ?
2/ how to send multipart emails (both html + plain text)

Can't find any explanation about these points...
Could somebody help me to solve this ?

Thank you by advance !
Cheers

re "1/": That's a setting in your SMTP mail server, nothing to do with Community Builder.

re "2/": iirc if you select to send mails in HTML format (where available), they are sent multipart (although that's getting less and less useful imho).

Hi !
Thanks for you answers !

1/ ok, I will check my settings with my hoster
2/ ok, but strange... as I receive emails only in HTML type... (in the header : Content-Type: text/html; charset=UTF-

My emails are sent with PHPmail (not SMTP).
CB settings are on HTML format, with a language string, so my messages (french and english) are located in HTML in the languages files.