Could be a conntrack issue related to your host over-selling vps resources, so the spikes of others bring some/everyone down at times. What kind of vps do you have? If you can, go for kvm vps, it is the next best thing to dedicated with guaranteed resources, though the data center practices still matter.If I used the DNS queries out of the limits.. the rest of Email won't be send out, am I understand correct?
But the error sending is mixed with successful sending.
It means I am out of DNS query and back to normal next minute?