Vivaldi Technolgies has both: the client "M3" ( which will be integrated in the Browser ) and the email service Vivaldi Mail.
Vivaldi Technologies has the Browser Vivaldi where the email client M3 will be integrated ( An email client - for example like Thunderbird -, a email reader or more formally mail user agent (MUA) is a computer program used to access and manage a user's email, it downloads your emails from any E-Mail service/provider you want ) This client named M3 they mean with soon (;
And then Vivaldi Technologies has also the webmail service Vivaldi Mail which you mean, like Gmail, Yahoo Mail - you can use it already when you are registered here: https://vivaldi.net
So yes, since Vivaldi Technologies offers Vivaldi Mail they are also an email service provider (;
You can log-in here: https://mail.vivaldi.net/webmail/
Or use the new more modern interface which will become soon standard: https://webmail.vivaldi.net
Enjoy it, the new interface of Vivaldi Mail is really nice and clear, no ads, no spying and the servers are located in iceland where the strict data privacy laws are very strong (:
Vivaldi Web mail https://mail.vivaldi.net/webmail/ is a service based in the Netherlands and is free and privacy minded and will not sell or look at your data.