Yes, you can! Although sending mail for multiple domains over a single account isn’t an ideal scenario since some of your emails will come from the IP address associated with your main account/domain. This can cause deliverability issues because of a mismatch in domains that are used in the email signature headers.
That said, it’s still acceptable to send “on behalf” of other domains, but it’s not best practice.
The general rule of thumb is to have one specific account and one specific IP for each domain you’d like to send from.