Issue CentOS - Emails being duplicated

[patDobson]

Server details: Version - Plesk Obsidian v18.0.31_build1800201209.09 os_CentOS 6 OS - CentOS 6.10 (Final)

I have a server set up on a 123reg VPS and at the moment for every email that's sent to it, two copies are recevied.

I've recently added a new site but the only setting I have changed is :

Tools & Settings / Mail server settings / [Enable mail autodiscover]

I've since switched that off but emails are still being doubled. It's not just the 'new' domain that's affected, it seems like all of them are.

Anyone got any idea how I can sort this out ?

*Update: Interestingly messages marked as spam are not duplicated...