Issue resolved by regenerating ssh keys and then testing.
[zimbra@mail ~]$ zmsshkeygen
Generating public/private dsa key pair.
Your identification has been saved in /opt/zimbra/.ssh/zimbra_identity.
Your public key has been saved in /opt/zimbra/.ssh/zimbra_identity.pub.
The key fingerprint is:
<fingerprint> mail.myserver.com
[zimbra@mail ~]$ zmupdateauthkeys
updating mail.myserver.com
Fetching key for mail.myserver.com
Updating /opt/zimbra/.ssh/authorized_keys
[zimbra@mail ~]$ ssh -i .ssh/zimbra_identity -o strictHostKeyChecking=no
zimbra@mail.myserver.com
Warning: Permanently added mail.myserver.com,<ip>(RSA) to the list of known hosts.
Connection to mail.myserver.com closed.