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Reject domains containing capital letters
MailCleaner Support
Added almost 4 years ago
Domain names shouldnt have any capital letters in them according to RFCs so we decided to forbid this use for sending domains as this is most of the time used to circumvant anti spoofing tools.
Since this is compliant to RFCs and since using those capital letters is mainly made to spoof addresses, we decided to activate it for everyone by default.
This feature is based on the recipient domains that is to say you can enable/disable this feature for any domain you are hosting.
To change this feature settings go to
Configuration->Domains-> -> Filtering
and check or uncheck
Reject domains containing capital letters
then restart the Incoming MTA for all servers of your cluster in
Monitoring status
To enable this feature on all domains of your cluster, you can run on the master node of your cluster
echo "update domain_pref set reject_capital_domain=1" |mc_mysql -m mc_config
change 1 to 0 if you want to disable it then to forget to restart your Incoming MTA.