Use the opensmtpd package as it was updated in guix

Julien LepillerThu Feb 20 16:45:42+0100 2020

20e2957

Use the opensmtpd package as it was updated in guix

modules/config/mail.scm

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(define (lepiller-smtp-service interface domain)
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  (service opensmtpd-service-type
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           (opensmtpd-configuration
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	     (package opensmtpd-next)
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             (config-file (opensmtpd-conf interface domain)))))
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(define (lepiller-dkim-service domain)