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I have an IMAP account on a private server and they said me to configure my mail with a STARTTLS secure connection on the port 993 and authentication with standard password.

How can I set STARTTLS in Mail.app?

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First of all, notice that port 993 usually does not use STARTTLS. If you have been told to use port 993 and STARTTLS, then that would be very strange indeed. The different between STARTTLS and ordinary SSL/TLS is the following: With ordinary SSL/TLS, which is what is usually used on Port 993, the connection immediately starts with an SSL/TLS handshake. In layman's terms, one may say that the connection is immediately encrypted. However, when using STARTTLS, which is usually used in combination with Port 143, the connection starts unecrypted. The first IMAP commands exchanged between client and server (including the STARTTLS command) are unencrypted. However, after the STARTTLS command, both client and server upgrade the unencrypted connection to an encrypted one. That means the SSL/TLS handshake is not done immediately, but only after the client has sent the STARTTLS command to the server. That's all.

Now sadly, I have experienced that Apple's Mail App does not support STARTTLS on Port 143 and seems to only support encrypted IMAP connections over Port 993 using SSL/TLS.

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I haven't tested this combination, but you should be able to enable it by creating the account as normal (be sure to use IMAP for mailbox access), then going into the Mail application's preferences -> Accounts section -> your account in the list -> Advanced tab, then setting the "Port" entry to 993 and selecting the "Use SSL" checkbox.

A couple of notes may clarify what's going on here:

  1. TLS is the new name for the SSL protocol (actually, for newer versions of the protocol); pretty much everywhere you see references to "SSL" they're really talking about TLS
  2. There are two ways of initiating TLS (/SSL) for a connection: either connect to a special SSL port and initiate the TLS setup immediately (for example, "http://" URLs connect to port 80, but "https://" URLs connect to port 443 and go directly into TLS setup); or connect to a normal (non-TLS) port for the service and then use the "STARTTLS" command to upgrade the connection to TLS encryption.

The second point is the only worry I have here. Port 993 is normally the special port used for the "imaps" service, the go-straight-into-TLS version of imap. But in this case it sounds like the server provides plain-then-STARTTLS service on port 993, which might confuse Mail.app. I suspect it'll work fine, but I don't have a similar server to test with, so I can't be sure.

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  • Thanks, actually that's what I did before. However it doesn't work. The connection doctor says "Trying to log in to this IMAP account failed. Verify that the username and the password are correct". Now, I'm sure that the password and the ID are correct. The only problem I can imagine is that the account is not yet enabled. Do you think with this error is for sure a problem of authentication or could be also a problem of connection?
    – Maverik
    Mar 16, 2013 at 11:22
  • +1 for the detailed response, even if it didn't work :)
    – zigg
    Jul 14, 2013 at 19:36
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TLS is NOT the new name for SSL. It's the new version of SSL. SSL had some serious security problems and then TSL was developed. There were some security issues with downgrade attacks from TSL to SSL, so they had to turn off the downwards compatibility to solve these issues

SSL 1.2 != TSL 1.2

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