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I have an instance of VPS running with logrotate that emails me logs every day. It is a send-only SMTP server with Postfix, set up using this guide. I just need to receive the logs from this server. Incoming email is on the different server that I use for communication.

It works great, however I have a concern if someone will intercept my logs, they might find out some vulnerable info about the server.

My questions are:

1) Is the outbound email secured when sending it like that?

2) What can I do to further secure the outbound emails? Encryption? Tls?

I do have a certificate from Let's Encrypt, but not sure if it will matter here?

Thanks in advance!

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1) Is the outbound email secured when sending it like that?

No. The setup you use is just a minimal setup and does not enforce TLS with proper certificate validation to the target mail server.

2) What can I do to further secure the outbound emails? Encryption? Tls?

The best is actually to encrypt the mails itself and don't rely on the security of the transport, because mail transport does not offer much security. For proper end to end encryption of mails use PGP and S/MIME.

I do have a certificate from Let's Encrypt, but not sure if it will matter here?

It does not really matter. Since you are only sending this certificate could at most be used as a client certificate to authenticate against the target mail server. In your current setup this does help. If you would use a fixed target mail server and would set this up to require and properly verify a client certificate then it might help.

But again, the easiest way to get better security is to use PGP or S/MIME to encrypt the message itself and not rely on the security of the transport.

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  • Thanks for your reply! Thats what I though, why would it be encrypted. I will look into encryption with PGP for all the emails.
    – Ilya
    Commented Mar 1, 2017 at 5:16
  • If you had complete control over the destination server, then you could required TLS between the two, and possibly also cert-based authentication. Then your email would be encrypted in transit. This does assume, though, that your email will transit - encrypting the email from the get-go means that even if it is stuck in a local spool, it should be safe (obviously, if that is a concern, the contents of the email might not be so important, considering someone is already on your box).
    – iwaseatenbyagrue
    Commented Mar 1, 2017 at 12:42
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It depends on how you trust the recipient mail server, and how is secure the network between the 2 hosts.

If the mail is not encrypted, everybody with administrator privileges on the mail server can read the mail. And everybody with administrative privileges on any component of the network between the two hosts could intercept it. That includes of course any SMTP relay, but also any smart router or bridge and any machine using promiscuous mode on a ethernet network.

So if the two host are in the same administrative zone you should not worry about it. If an encrypted VPN exists to make them logically in the same lan and you trust all machines of that lan, unencrypted exchanges makes sense too. In any other case, you should encrypt the logs before sending them by mail.

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