When resellers generate a ticket or a new user, an e-mail will be sent automatically. You can configure the sender of these e-mails in your reseller account.
Login to DirectAdmin
First login to DirectAdmin, click 'User level' on your right and then click any domain name. It doesn't matter which domain name you click.
Click Site Summary / Statistics / Logs". Op this page you can configure the name and e-mail address.
For instance, under 'Name' you can say 'WebdesignCompany' and under 'E-mail' you can say 'email@example.com'.