Exim MTA configuration

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extern val handleMail : [Domain] {MailNodes : [mail_node]}
extern val relayMail : [Domain] {MailNodes : [mail_node]}

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extern val handleMail : [Domain] {MailNodes : [mail_node]}

The specified nodes should handle mail for this domain.

extern val relayMail : [Domain] {MailNodes : [mail_node]}

The specified nodes should relay mail for this domain. That is, they should forward it on to authoritative mail servers, not handle it locally.