Entering data of co-authors without e-mail address

We want to submit several proposals on behalf of their authors, but we don't have the e-mail addresses of all co-authors, how do we proceed?

Can we disable the e-mail field from the paper submission form?

It is not possible to disable e-mail fields for the author once contributions have been submitted. We also do not recommend to create a new track without the mail address field enabled, as the address is used to link user accounts to the co-authors of submissions.

Instead please simply enter the e-mail address of the submitting author (see image) for all co-authors with unknown e-mail addresses.