A few hints: smtpd listens for incoming messages (port 25 or 587) inbound to your box. It's possible your local MUA will connect to 127.0.0.1:25 or 127.0.0.1:587 to send mail, or it may invoke /usr/libexec/sendmail. This service is somewhat confusingly listed as smtp in master.cf. There isn't a separate smtp config file; it's config items of the form smtp_ in main.cf I haven't ever done what you are trying, but the following may be helpful: smtp_sasl_password_maps = hash:/etc/postfix/saslpasswd (saslpassword is going to a mapping from hostname to username and password, somehow) This is probably helpful; it looks sensible given the other things I've seen: https://wiki.zimbra.com/?title=Outgoing_SMTP_Authentication
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