Custom sender email means that you can use your own company domain, e.g. email@example.com or even your own email as sender email.
In this case, we prepare everything, but your admin needs to also make some adjustments.
As a second option, we can set up a new domain, e.g. yourcompanydomain-events.com which can be used as sender email, e.g. firstname.lastname@example.org. In this case we can take care of the setup and your IT does not need to be involved.