As a user of Mailjet, I would like the ability to add complete domains to (sub)accounts in bulk.

Currently the way to do it is to do this per 1 domain. You first have to validate it, then you get forwarded to the screen for SPF/DKIM.
I know you can theoretically setup SPF/DKIM ahead of time as this is the same for all the domains.

However, as a customer with many domains, I would like the ability to add for example ~25 domains in one go. Then provide me all the validation TXT-records, and validate them in the background.

This is already possible via API, so this should also be possible for the frontend.