Hi @Timothy Fong39.
You can change the sender of the email from Admin Settings> Settings> Access:
The "From" email address for the notifications is set by default on no-reply@YourCommuntiyURL.
You can add a customized email address here and save the changes. This way. all the notification will be sent from this email. You need to make sure to prevent the email notification from being recognized as spam, you use the email with the same domain that you have for your community URL. If you have not moved the community under your own domain or sub-domain18, please make sure you do.
For the "welcome email app", you need to insert the "from email" in the app settings as explained here20.