TLS Enable

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To enable TLS for communications to and from a domain you need to add the TLS info to CanIt for that domain. It requires editing /etc/mail/access on all machines and running "make -C /etc/mail" to update the binary database.

This is a Sendmail function. First, you need to make sure that STARTTLS is enabled on your server. You do that by putting this line:


in /etc/mail/ somewhere before the MAILER(`local')dnl line.

Then type:

   make -C /etc/mail && /etc/init.d/sendmail restart

You need to do this on all hosts. To make sure it's working, telnet to your machine on port 25 and type:

   EHLO test

If it is working, you should see "250-STARTTLS" in the server's response.

Next: To force Sendmail to use TLS for a specific domain, edit/etc/mail/access (on all hosts) and add these lines:     ENCR:168     ENCR:168

and type:

    make -C /etc/mail && /etc/init.d/sendmail restart

This means that all connections to must be encrypted with at least 168 bits of key. You might need to check with to find out what key length they want or need. The TLS_Srv is for outbound mail and TLS_Clt is for inbound email.

NOTE: If Sendmail cannot negotiate an encrypted session with, all mail to or from that domain will bounce. So be sure to get the required key length correct by asking what it should be!

The details are here:

Testing TLS in CanIt

If you see log lines similar to this:

  2014-05-26T00:00:00.588066-04:00 colo10 sm-mta[14920]:
  STARTTLS=server, [],
  version=TLSv1/SSLv3, verify=NOT, cipher=DHE-RSA-AES256-SHA,

Note: STARTTLS=server means CanIt is acting as the server.

It means that an encrypted connection has been negotiated. The verify=NOT means that we didn't ask the connecting server for a certificate. The cipher=DHE-RSA-AES256-SHA indicates the chosen cipher, and the bits=256/256 indicates that an encryption key of 256 bits was negotiated out of the strongest possible 256 bits.

If you see something like this:

  2014-05-26T00:00:01.974059-04:00 colo10 sm-mta[14924]:
  version=TLSv1/SSLv3, verify=FAIL, cipher=AES128-SHA, bits=128/128

STARTTLS=client means CanIt is acting as the client. It means that we succesfully negotated a 128-bit encrypted connection using the AES128-SHA cipher to, but we failed to validate its SSL certificate. (We still encrypt anyway... that's opportunistic encryption.)

It should be safe to enable STARTTLS on all your cluster members.