I want Postfix to proxy SMTP connections from MUA on my client to another outer SMTP server.

Since the outer SMTP server requires the Postfix proxy to authenticate with SMTP-AUTH, So I set my MUA's credentials into the proxy in /etc/postfix/sasl_passwd and configure smtp_sasl_auth_enbale = yes and smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd in /etc/postfix/main.cf.

After postmap /etc/postfix/sasl_passwd and systemd restart postfix, I can send a mail and safely receive via the proxy.

But from the point of my client, it is not natural that the credentials are placed on the proxy server.

So please tell me how I can pass through the credentials themselves without saving them on the proxy.

The Postfix proxy is run on Ubuntu 15.04.

Can anyone be of help?


This really isn't the way SMTP is designed to work. The postfix you are configuring is not really a 'proxy', it's actually a relay, which is expected to accept the mail from your MUA in one connection, then send it on to the next hop in a completely independent connection (potentially quite a bit later, depending on whether the next hop is even available right then).

If the 'outer' SMTP server needs authentication, your options are what you've done so far with SASL config in postfix, or have your MUA connect directly to the 'outer' SMTP server.

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