Copy of incoming Mail (Mac "Mail" is client) shows up in sent email when email is sent from a php form after migration to g suite

I helped someone migrate their email from a web hosting service because of deliverability issues. Anyway, the migration went well:

• Migrated email
• Set mx records
• Authenticated domain name (SPF and DKIM)
• Implemented DMARC (reporting only for now)
• Added accounts to their Apple Mail and mobile email client

Email sent from a PHP form that sends an email whenever a new order comes in arrives in both the account inbox but also a copy of it arrives in the subfolder for the account" user and the important user so it's three places for email. The email is basically an orders notification that summarizes the order so they know there's an order to be fulfilled (it's a physical product that needs to be shipped).

I helped them do a rule that said if To contains orders@ then move to orders folder and applied to existing email. It worked on existing email but the rule doesn't run on new orders coming in.

The rule wasn't meant as a permanent solution anyway, but as a stopgap, until I could find the root cause. Any ideas on why this rule doesn't work on new emails? And any ideas on the root cause of this and how to solve it so the email does not show up in 3 folders? It's a lot of clutter is the issue.

addendum

I've noticed that the form sends from [email protected] so maybe the reason this is happening is that is the same address as the account the form submits to. So google thinks that since the email is "From" the same account that's being sent to it thinks it must have sent it so it puts a copy in sent. I think that might be what's happening. Now, I'm wondering if there's a way to work around that so emails "from" the orders@ address are identified only as incoming emails for the inbox not as a sent email as well. Any ideas on a way to do this if my hypothesis makes sense as a possiblity?