Email not arriving in 1and1 Mailbox sent via Mandrill - DNS, MX, SPF, DKIM?

In short email sent via Mandrill app to 1and1 email accounts are not arriving yet they arrive to other types of email accounts.

The long version…

My domain, e.g. domain.com, is registered with 1and1, the name servers point to DO (ns1.digitalocean.com etc.)

In the DO DNS Control Panel, I have set the MX records back to 1and1 so that I can use their email.

For transactional emails on the website, I have configured the site to use Mandrill and set the appropriate SPF and DKIM record in the DO DNS Control Panel. This verifies as correctly configured in my Mandrill App.

The website sends transactional emails via Mandrill as it should according to the reports in Mandrill. They are sent via orders@domain.com and arrive to the customer.

The problem is that they dont arrive to any other email addresses on the same domain (order confirmations, refunds etc. ).

For example they don’t arrive in the following:

orders@domain.com -> myemail@domain.com orders@domain.com -> me@domain.com orders@domain.com -> xxxx@domain.com

These emails arrive fine to my other email addresses, e.g. @gmail, @yahoo, @btinternet etc.

I think 1and1 believes these emails are spam as they dont originate from their servers and is blocking them.

1and1’s support is 0 help. I have emailed them over 10 times now with no suitable response or resolution.

I am absolutely stumped about how to proceed with resolving this.