howto/email.md
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+Running email in dn42 is not very complicated. Your SMTP daemon probably already listens on the wildcard address, so you mostly need to:
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+
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+* open your firewall to allow TCP/25 from dn42
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+* setup DNS (MX records, or simply relevant A records)
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+* configure your mail server if needed
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+
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+## Exim tips
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+### Sending emails
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+By default on Debian, Exim refuses to send mail to other mailservers when they resolve to RFC1918 addresses. This will manifest by the following error message when trying to send a mail:
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+ ** foo@bar.dn42: all relevant MX records point to non-existent hosts
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+This is controlled by the `ignore_target_hosts` variable in the configuration file.
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+
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+### Receiving emails
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+Don't forget to add your dn42 domains to the list of local domains, so that you accept incoming emails. On Debian, it is controlled by `dc_other_hostnames` in `update-exim4.conf.conf`. For instance:
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+ dc_other_hostnames='myself.org;myself.dn42;myserver.myself.dn42'