I have recently successfully managed to get a Postfix/Dovecot setup working with a RELAY (no credentials) provided by my ISP since they block all outbound traffic on port 25.

Question is how secure and private is this setup?

I have setup a test account in Thunderbird, which uses port 993 for pickup (SSL/TLS, Normal password) and port 587 for mail submission (STARTTLS, Normal password) from Thunderbird to my outgoing server. This seems secure so far, correct me if I'm wrong.

However, it seems to me that the use of a relay defeats the whole structure of privacy. Can my ISP see the contents my emails I send out and receive through this relay? If I switch to another host that does require credentials to use it (Eg. smtp.gmail.com), would Google be able to see the contents of my emails?

What would be the most private setup in this case?

2 Answers 2


Yes, currently your provider sees both inbound and outbound messages in plaintext at some point.

And yes, switching to gmail, you would give these accesses to Google instead.

You could want to setup your own public relay, starting by registering your own domain name, defining a few A and MX records identifying your mail server public IP for everyone to see. Which requires being able to create outbound connections to TCP port 25 (as not every SMTP server listens on SMTPS).

  • I do this. You can also use OpenVPN, tinc or many other open source VPN's to allow sending the mail from your public relays to your home automatically, without opening any inbound ports to your home. That way the relays are just simple dumb machines that don't store anything. I force TLS on but not everyone supports that yet. Most do that I care about.
    – Aaron
    Nov 14, 2016 at 5:35

If you do not want the content of your emails to be read, encrypt the contents body, not the means you use to transport it (SSL).

Even if you do as @SYN says you lose control of the transport of the email as soon as it leaves your relay and hits someone elses.

They may secretly relay it elsewhere and store it, for example.

Email in its default form has never been secure and offers no expectation of privacy. Dont send anything through it you wouldn't be willing to shout down the street to someone.

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