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Debian disable ipv6
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Unless you have configured a firewall that addresses ipv6 networking you should disable ipv6.


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/etc/sysctl.conf
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net.ipv6.conf.all.disable_ipv6 = 1


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sysctl -p


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/etc/exim4/update-exim4.conf.conf
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dc_eximconfig_configtype='satellite'
dc_other_hostnames='host.domain.com'
dc_local_interfaces='127.0.0.1'
dc_readhost='host.domain.com'
dc_relay_domains=''
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost='smarthost.mailhost.com'
CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname='true'
dc_mailname_in_oh='true'
dc_localdelivery='mail_spool'
disable_ipv6='true'

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update-exim4.conf

systemctl restart exim4


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done
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