Hi @BookkeepingBecky 

The only thing you can check is that your email address is set correctly in the contact detials section of https://app.qbo.intuit.com/app/accountsettings 

If Send-as-Domain is really available in QBO Advanced (I'm 99.9% sure it isn't & the support staff are wrong or using confusing language or stalling for time while the system comes back online) then there will be a setting in there to turn it on/off & revert to using quickbooks<@>notification.intuit.com because not everyone will want or need it.  Certainly not everyone will be able to configure it correctly because the SPF/DKIM settings can be quite complicated.

SMTP is something different - these settings were available in the old QB Desktop I think (later versions would only work by piggybacking onto MS Outlook though).  Using SMTP would require entering your email address & password into QBO Settings.