Most visitors to this page are probably aiming to get their CanIt server to offer STARTTLS. If that is the case, please visit this page:
NOTE: After following the page above, you may still need to follow the steps to add the
/etc/mail/tls/starttls.m4 include line to your
/etc/mail/sendmail.mc file. (those steps are on this page but are also included on the above page)
TLS settings for specific domains
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.
Enabling TLS in sendmail.mc
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/sendmail.mc somewhere before the MAILER(`local')dnl line.
NOTE: Look closely at the beginning:
include(`. Notice the next character after the open bracket is a back-tick (tilde key near ESC on most 105key US keyboard layouts). This is important. Also note, if you copy-paste from above your copy-paste may convert the back-tick to a single quote. Watch out for this.
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:
If it is working, you should see "250-STARTTLS" in the server's response.
The details are here: http://www.sendmail.org/~ca/email/starttls.html
Testing TLS in CanIt
If you see log lines similar to this:
2014-05-26T00:00:00.588066-04:00 colo10 sm-mta: STARTTLS=server, relay=mail.example.com [192.168.1.1], version=TLSv1/SSLv3, verify=NOT, cipher=DHE-RSA-AES256-SHA, bits=256/256
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: STARTTLS=client, relay=mail.example.com., 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 mail.example.com, 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.