A problem we get with using the addressbook is that we don't have an easy way to deal with multiple addresses.
I therefore started to question whether we shouldn't rather just autocomplete email-addresses.
We could still supplement the email address with information from the addressbook (avatar, name, ...), but perhaps building a solution that is geared towards email addresses works better?

I'm open to suggestions how to do that with the addressbook though.
One possible way would be to duplicate addressbook entries per email address, giving them a good way of differentiation for different email addresses.

the other solution would be a two step process of selecting the person and then pic an address if there is more then one. I'd like to avoid additional steps where possible though.

True, but I agree that adding more steps doesn't seem like a good idea for autocompletion. One benefit of the addressbook approach might be that it is much more touch-friendly than a list of email addresses (due to larger hitboxes).

We're doing simple string autocompletion for the addressbook now.