550 “REJECTED – Bad HELO exim error

This error may cause for some domains those MX record pointed to different domain.

In this case first check the MX record of the domain and see if it is in the same server.

If not remove the entry for the particular domain from the file,

/etc/localdomains

Then add the entry that you removed from the above file to the following file,

/etc/remotedomains

After this restart the exim service, It should be fine now.