If your email notification was triggered by an Abuse Detection rule, then you unfortunately can't customize the From address of the notification. However, I do agree that that functionality would be beneficial. This has been requested in the past, and may be available in a future version of SmarterMail. However, it doesn't seem that we have a Community thread for this request. I'm going to change this one to a Proposed Idea, so we can facilitate tracking on this one.
In the meantime, I have a workaround you should be able to use, though it may seem a little silly. You're able to configure the From address for emails that are sent from system Events, so you could create an event that will trigger an email when your abuse detection email is received. For the event type, choose Message Received. For the Conditions, set the To Address as the same email address that's configured for the "Email to Notify" field of the Abuse Detection rule. Set the subject to equal "Auto spam notification". For the Action of that event, pick Send Email. For the From Address, set the email address of your choosing. And for the To Address, enter the same email address that's used for the "Email to Notify" field in the Abuse Detection rule.
When your abuse detection rule is triggered, an email will be sent from the System Administrator to your spam folder. This delivery would then trigger the event you just created to deliver the same notification text to your Inbox.
It's a little convoluted, but I hope this helps!