Backup MX configuration with Exim

[tobiascapin]

Dear sirs,
I'm working on a MX temporary Backup to turn on during the main MX maintenance.

I installed Exim4 with a very simple configuration:

dc_eximconfig_configtype='internet'
dc_other_hostnames=''
dc_local_interfaces=''
dc_readhost=''
dc_relay_domains='mydomain.com'
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost=''
CFILEMODE='644'
dc_use_split_config='true'
dc_hide_mailname=''
dc_mailname_in_oh='true'
dc_localdelivery='maildir_home'

I just left empty local_domain and filled relay_domains with my domain.
Moreover I add my backup server to MX records with high priority value (50).

Should I do anything else?
May my backup can suffer of mail loops because when it tries to process the queu will find itself in MX records?