root@xxx:/etc/opendkim/keys/domain1.com# opendkim-testkey -d domain1.com -s mail -k mail.private -vvv
opendkim-testkey: using default configfile /etc/opendkim.conf
opendkim-testkey: key loaded from mail.private
opendkim-testkey: checking key 'mail._domainkey.domain1.com'
opendkim-testkey: key not secure
opendkim-testkey: key OK

root@xxx:/etc/opendkim/keys/domain2.com# opendkim-testkey -d domain2.com -s mail -k mail.private -vvv
opendkim-testkey: using default configfile /etc/opendkim.conf
opendkim-testkey: key loaded from mail.private
opendkim-testkey: checking key 'mail._domainkey.domain2.com'
opendkim-testkey: 'mail._domainkey.domain2.com' record not found

Syslog                  yes
OversignHeaders         From
AutoRestart             Yes
AutoRestartRate         10/1h
UMask                   002
SyslogSuccess           Yes
LogWhy                  Yes
Canonicalization        relaxed/simple
ExternalIgnoreList      refile:/etc/opendkim/TrustedHosts
InternalHosts           refile:/etc/opendkim/TrustedHosts
KeyTable                refile:/etc/opendkim/KeyTable
SigningTable            refile:/etc/opendkim/SigningTable
Mode                    sv
PidFile                 /var/run/opendkim/opendkim.pid
SignatureAlgorithm      rsa-sha256
UserID                  opendkim:opendkim
Socket                  inet:12301@localhost

#DKIM config
milter_protocol = 6
milter_default_action = accept
smtpd_milters = inet:localhost:12301
non_smtpd_milters = inet:localhost:12301

domain1.com mail._domainkey.domain1
domain2.com mail._domainkey.domain2

127.0.0.1
localhost
x.x.x.x    #IP SERVER
y.y.y.y    #IP FAILOVER domain1
z.z.z.z    #IP FAILOVER domain2
ns123456.ip-X-Y-Z.eu #SERVER NAME
domain1.com
domain2.com

mail._domainkey.domain1.com domain1.com:mail:/etc/opendkim/keys/ domain1.com/mail.private
mail._domainkey.domain2.com domain2.com:mail:/etc/opendkim/keys/ domain2.com/mail.private