In our hosted environment, we utilize a robust email system that will deliver email to any recipient. However, while the email is being delivered with a "Send From" address with your own district email domain, the message is physically coming from us. This requires the district to create a SPF record (or append an existing record) which will contain the following host name _spf.aeries.net.
In order for an SPF record to be effective, it is important to use a real domain name* in your "Send Emails From" setting in the Portal Settings section of the School Options page. If you are using Online Enrollment (AIR), you will also need to verify the same setting there, too.
Do you need help identifying what your domain's current SPF record looks like? Try MXToolbox's SPF Lookup!
SPFWizard (SPF record builder): https://www.spfwizard.net/
* If you do not have control over your domain name's DNS record, you can always use "DoNotReply@aeries.net" as your Send Emails From address.