Email invoices fail to deliver - 'Diagnostic-Code: rejected'

Email invoices - "Diagnostic-Code: rejected"

I'm working with a business that is unable to receive MYOB invoices/statements from their supplier.

Looking at previous forum posts (1) (2), it seems these people were able to remove the address from a blacklist and/or add it to a whitelist. 

Can I request a DM to provide customer details/email address to investigate?

Email from MYOB below

    From: [removed] <bounce@apps.myob.com>
    Sent: 22/5/2025 4:17 pm
    To: [removed]
    Subject: Undeliverable: Invoice [removed] From [removed]

    Sorry, email delivery was unsuccessful.

    Subject: Statement From [removed]

    Destination: [removed]

    Sent: May 22nd 2025 4:08:26pm

    Message: [removed]

    Diagnostic-Code: rejected