Undeliverable email and Unverified Sender on Desk tickets logged by email

Undeliverable email and Unverified Sender on Desk tickets logged by email

We have recently changed over mail servers and had to re-arrange our mailboxes and aliases in each and since that time testing of tickets we have raised via email to Zoho Desk have been failing and not been created.

We have several departments set up in Desk each with their own support email address and correspondingly I have email accounts set up under our domain topleftdesigns.com.au set up as email accounts or as an alias under one of those accounts. We have SPF, DKIM and DMARC records in place.

All support email addresses are set up under a single email account as aliases. This account has a forwarding rule set to send incoming emails through to the Desk Support Email address.

What I have fund is the following:
  1. Emails sent directly from any of our own email accounts to any of the support 'From' email addresses we set up come back with an Undeliverable Mail Returned to Sender (see one attached)
  2. If I go into the mailbox for one our support email addresses I can see the message and if I then Fwd this to the relevant Desk Support email address (xxx@myaccount.zohodesk.com) for the relevant department the ticket is created but shows with an Unverified Sender message
  3. If I send an email from my an email address that is for an existing Contact record in Desk to the Desk Support email address (xxx@myaccount.zohodesk.com) the ticket is created just fine.
  4. I sent an email from a Gmail address directly to our support mailbox and this went through OK creating the ticket in Desk
It would seem that the problems relate to tickets sent from our own domain email accounts yet all the DNS records check out OK as far as I have been able to determine.

Can you please advise on how I can fix the Undeliverable