It's strangely difficult to find out exactly how SSL works with email, at least insofar as answering my specific question - when I connect to gmail using SSL, I understand that my connected is secure and thus data is all encrypted between MY COMPUTER and the GMAIL SERVER. However, is that all SSL does? For example, when I open an email on my computer, the data between Mountain View (or whatever) and my house is encrypted? Would that mean then if I email my friend who also uses gmail with SSL/secure gmail enabled, then if I send an email also with an attachment to his gmail account that email as well as the attachment are encrypted at my computer, sent to GMail server, and then provided my friend uses SSL then he can security acquire the email too? So there is no need for those firefox encryption addons? Are those just for more robust encryption algorithms?

So in summary, here is what I think I have learned (and provides a summary for others reading). PLEASE CORRECT ME IF I AM WRONG:

  1. gmail sends emails to google servers with HTTP. gmail also retrieves emails from google servers with HTTP. when you connect to the google servers using https (as opposed to http) then the connection between your gmail client and the gmail servers is secure and data is encrypted going back and forth between the two.

  2. when using a client (thunderbird for example) SMTP is used to send emails, and IMAP/POP are used for retrieving emails. At the add-on/options level, you can tell these clients to use TLC for both the SMTP and IMAP/POP steps.

  3. The google servers probably don't use TLS with SMTP when bouncing emails back and forth amongst their servers.

  4. Conclusion - if using gmail, always use HTTPS but know there is no encryption between google's servers, but in the 'outside world' the connection between google clients (as long as using https) is secure. if using thunderbird (or something else) turn on TLS.

Is this correct?

3 Answers 3


When you trust the certificate from the site encrypted with SSL, you can:

  • Trust that the connection to that web server is encrypted.
  • Trust that the identity of that web server is correct (ie its not phishing scam).
  • Trust that someone isn't intercepting your traffic to the web server (man in the middle).

(the important thing here, of course, is that you trust the certificate presented by Google's mail server, which you generally should :-))

The data you submit in a form when composing an email will be encrypted through HTTPS as it travels from your client browser to the Gmail server that will pass it off to the SMTP server. When you display mail in your browser from the server, this is also encrypted.

SMTP does not encrypt mail, however. There are ways to use TLS (transport layer security) over IMAP and POP to encrypt the authenication data from the user/client to the server. When you connect via IMAP/POP with TLS, the data you receive when retrieving mail is encrypted from the server to you. IMAP and POP are retrieval protocols only. When you use an external client such as Thunderbird to send mail, it will go through an SMTP server. This can be encrypted as well using SASL/TLS with SMTP, but again that is only from your client to the server, and not from the server to its final destination.

If you want to send and receive encrypted email end to end, no matter where it goes on the network, then you need to look into a solution like PGP/GPG. For more information about this, see the question I asked. Gmail's webui doesn't support usage of PGP/GPG, so you'll need to set that up with an external mail client such as Thunderbird, Mail.app, or Outlook (or others).

As far as email you send from your Gmail account to a friend's Gmail account, it is sent around inside Google's internal mail infrastructure. This may have one or more hops between servers, but usually stays within their private (10.x.x.x) network. You can verify this by looking at the headers of the email your friend sends. From the email in the Gmail webui, hit the drop down button next to the "Reply" and click "Show Original". You're looking for lines that start with "Received:", like these:

Received: by with SMTP id p12cs100615qai;
        Sun, 18 Jan 2009 15:04:17 -0800 (PST)
Received: by with SMTP id x20mr2195513agb.12.1232319857088;
        Sun, 18 Jan 2009 15:04:17 -0800 (PST)
Received: by with HTTP; Sun, 18 Jan 2009 15:04:17 -0800 (PST)

This is a Gmail to Gmail message I have. The first (last) message here indicates that the mail server received the message in question from an HTTP connection (webui). Then the mail went via SMTP to, then SMTP to, where it was delivered to me.

Again, while this is all internal to Google's network, SMTP should not be considered a secure protocol for sending sensitive information. Anyone who has access to the systems in the chain above can potentially read the message. Also note that Google Apps may go through a gateway system on their network that has an external address (still owned by Google, though).

  • I will add one caveat the SSL would prevent a man in the middle phishing scam but it is not guaranteed to prevent a simmilar name phishing attack.
    – EBGreen
    Aug 19, 2009 at 14:15
  • so if I understand this, SSL provides a secure HTTP connect (hence https), but email is not sent over HTTP, it is sent over SMTP, and THAT is not encrypted by SSL?
    – Tony Stark
    Aug 19, 2009 at 14:23
  • 1
    so SMTP may not be a secure protocol, but when SSL is set up, does that cover SMTP too? And IMAP and POP would not not be covered/encrypted by SSL?
    – Tony Stark
    Aug 19, 2009 at 14:29
  • @hatorade I clarified in the sentence after the bullets, and expanded on those.
    – jtimberman
    Aug 19, 2009 at 14:29
  • @hatorade I also clarified about imap/pop. I hope this answer helps, good question!
    – jtimberman
    Aug 19, 2009 at 14:34

Your data is not secure.

People are always worried about the data in transit, but the basic fact is that the data storage is the main point of where attacks happen. E.G. Credit cards generally get stolen from files and databases of numbers, and not from the transport of the numbers.

Google stores your data. The storage is not encrypted. People at Google, or those who compromise Google can one day read it, if they actually care to. The recipient of the mail can also read it, and the owner of the recipient's mail server (ISP or company) can too. If the recipient is using a regular mail client, it is stored on his/her machine. This is where any spyware or rootkits that the recipient has installed could get at it.

In transit, jtimberman is right. Your browser is talking to Google, if you trust that the machine that sent you the certificate is Google, and that Verisign or whomever is a trustworthy company which tells you that Google did actually send you Google's certificate. While the browser talks to Google with the certificate over https, the transmission is encrypted. This is nice, because it means that all the other PCs on your network with possible spyware or nosey-users, and the network admin, cannot read how much you complain about them every single day.

You also have to trust your browser, AND all it's plug ins. They can pretty much just read what's in the forms before you even sent it. Generally you can trust it, but not those nosey tool bars everyone is asking you to install along side all those free programs you download.

But overall, say you sent someone an email and it contained your tax-id, birthdate, current address and legal name, something an employer maybe needs to know, you'd think of that as sensitive information. Well that email is stored forever by Google in the sent-mail area. Even after you delete it. And the recipient is going to store a copy in their inbox. The mail server of the recipient could be storing a copy. The mail-server of the domain of the recipient's mail-server could be storing a copy, but not for long. And a number of more servers in between. ALSO smtp sends mail between these quite unencrypted, but what's scarier, that some criminal's malicious program might be listening to the right network at the right time to catch the data in transit, or that some other criminal's malicious program might one day get installed on any of the machines that now contain a copy, find that copy, then send the data to the criminal's organization?


GMAIL's SSL encryption does only protect your data in transit. So in your example of your e-mail message going from you to gmail and then from gmail to your friend, all of the transmissions would be encrypted, however, the data at rest on the gmail servers (a copy in your sent items and a copy in your friends inbox) would all be readable data. If you trust google to keep your data safe, then you are okay.

Which of the firefox add-ons are you thinking of?

jtimberman is right that you would need a 3rd party program like pgp/gpg to encrypt your mail messages so that Google couldn't read them.

  • so SSL would encrypt both HTTP data sent over my connection as well as SMTP data?
    – Tony Stark
    Aug 19, 2009 at 14:25
  • @hatorade, SSL only encrypts the traffic between your browser and GMail's web server. From there on, you can't know if anything is encrypted or not.
    – gustafc
    Aug 19, 2009 at 14:43
  • @sacryan I was going to use FireGPG
    – Tony Stark
    Aug 19, 2009 at 15:08

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