We are working in odoo.sh with multiple company.

now we are using odoo default mail server to send the Mails, which is too slow and not sending on the time scheduled.

So here we need to setup an outgoing mail server , we need to use the one where our domain hosted.How can we do that?. And how will that effect other company on setting the outgoing mail server?

Eg: we set outgoing mail server for company A ,ad@gmail.com and for company  B,will it use the same ad@gmail.com to send their mail too?