How (in)secure is POP/IMAP/SMTP

Question

I'm making a few assumptions about basic email security, and I want to confirm or clarify some of these points to make sure I understand the big picture. Please correct me where I'm mistaken:

The answer to this question gives some insight, but doesn't cover all I'm looking for.

This is all assuming a traditional email service, accessed using a desktop or mobile client, over POP or IMAP, and SMTP (ignoring webmail).

Suppose I'm retrieving messages - my client app passes my username and password to the POP server, which authenticates me, and sends back the messages. If I'm not using SSL/TLS, then the entire conversation, including the message and credentials, is in plaintext. And anyone watching the network traffic can intercept the entire thing. And if I am using SSL, then the entire conversation is safe, even over a public network. Do I have that right?

My understanding is that traditional messages are insecure when my server talks to someone else's server - so the message itself is likely vulnerable while in transit between servers, but at least with SSL my email password would be safe.

If I understand, PGP or similar would mean that the message itself is encrypted, so that as long as my and the recipient's private keys are safe, nobody else could read the message. But that's just the message, right? Not the IMAP/SMTP/POP connection? Meaning if I used PGP for the message, but a non-SSL connection to SMTP, I'd still be sending plaintext username and password to authenticate.

Basically, I'm trying to understand why an email provider would refuse to offer SSL/TLS for POP/IMAP/SMTP connections - one particular provider says they don't do it because email is inherently insecure anyway, so SSL doesn't actually do anything to protect you, and they suggest PGP for truly secure email. I'd like to argue that while SSL may not be end-to-end message protection, it would at least protect my credentials and protect my message for a significant portion of its journey (me to SMTP server, and POP server to recipient assuming they're connecting with SSL).

Do I have everything straight with that?

Answer 1

To answer your question:

• If you're using SSL/TLS to access your e-mails, regardless of whether it's POP or IMAP then it would be very difficult for anyone to decipher the text of the e-mails from analysing the traffic alone. That said some large companies e.g a law firm I used to work for have a server which sat between us and the internet, stripping out the SSL so the answer is a qualified yes in saying you're safe.

• Also if the message is still sitting on the e-mail server after you access it, then it is possible for your e-mail provider to be bribed/coerced into handing it over. Of course GPG does solve this problem. You can also ask your e-mail provider to delete messages you download through POP though you have to trust that they're both able and willing to delete the messages securely.

• With SSL, when logging in using your e-mail password, your password cannot easily be read by intercepting the traffic between your computer and e-mail server subject to the proviso I mentioned in point one.

• Your understanding of PGP is largely correct. If a message is sent to you encoded with your public key then only you our someone who has broken your private key can read it. The sender's private key is irrelevant as he can't use it to decode a message meant for you. If your e-mail password were sent in plain text though you're absolutely right in thinking it could be intercepted and someone could access your e-mails or send them on your behalf pretending to be you. If you used PGP at all times to encrypt and sign all messages and others did the same for you, this would protect the content of your messages though.

• I can't imagine why an e-mail provider wouldn't want to offer SSL beyond sheer laziness. You can even get free certificates these days! Most of the free webmail providers offer SSL e.g Gmail, have you thought about using them?

Answer 2

Suppose I'm retrieving messages - my client app passes my username and password to the POP server, which authenticates me, and sends back the messages. If I'm not using SSL/TLS, then the entire conversation, including the message and credentials, is in plaintext.

Not necessarily. SMTP, POP, and IMAP all can support multiple authentication mechanisms, some of which are encrypted (e.g., CRAM-MD5, GSSAPI). See a good list here under Non-plaintext authentication. In this manner, your credentials might be safe on the wire even though the actual mail isn't.

And if I am using SSL, then the entire conversation is safe, even over a public network. Do I have that right?

Yes, you do. However, as was pointed out in the thread you quoted, mail involves many hops. You may secure the client to the mail store server, but the path the mail takes from the sender's client to your mail store isn't provably secure unless you're using an end-to-end encryption mechanism.

Basically, I'm trying to understand why an email provider would refuse to offer SSL/TLS for POP/IMAP/SMTP connections

Because they're cheap, lazy, and nobody had to wear helmets on bikes when they were kids.

I'd like to argue that while SSL may not be end-to-end message protection, it would at least protect my credentials and protect my message for a significant portion of its journey (me to SMTP server, and POP server to recipient assuming they're connecting with SSL).

Yes, especially where those credentials are probably good for something else, such as managing your account with that provider.

Do I have everything straight with that?

Essentially, yes.

I would suggest, though, that you are wasting your time arguing with your provider about it. If they don't want to provide SSL, then find another provider. That's probably the only vote you could cast that they'd actually listen to.

Answer 3

This question has been pretty well answered. But, it's worth taking a look at the delivery from the sender's outgoing SMTP server to the recipient's incoming MX server. This delivery is often done using STARTTLS to encrypt the SMTP connection. With STARTTLS, the connection starts off in plain text, then the connection is upgraded to an SSL/TLS connection if both sides support it. However, there are inherent problems with SMTP and STARTTLS that make it possible for an active attacker to perform a MITM attack. See this article for more info.

Answer 4

As touched upon in this thread, SSL secures emails you have received only while in transit between the pop server and your machine , as well as those you sent only while in transit between your machine and the server smtp.

as stated by Stryfe, once sent the email arrives on the SMTP server, there is no evidence that the rest of the transit is secure until POP server of the recipient. Same thing on recipient side, where the path between your recipient machine and the email server is not secure; e.g. consider the case where the pop/imap server is in-house and an it team can have a look.

as for PGP mentioned couple of times; for having trying it, PGP is not easy to set up at all in enterprise with outlook, thunderbird, gmail and smartphone users. There are solid alternatives like CryptoMailer(http://www.thegreenbow.com/cryptomailer), although this one is immensely easier to setup and use.