smtp - Sendmail relay authentication

I'm trying to set up my sendmail to authenticate against a relay (comcast). I'm not seeing any attempts to authenticate at all. I'm trying to just debug how authentication works, and can't connect all the pieces...

I have, in my .mc file:

define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
define(`SMART_HOST', `relay:smtp.comcast.net.')dnl
define(`confAUTH_MECHANISMS', `PLAIN')dnl
FEATURE(`authinfo',`hash /etc/mail/client-info')dnl

And in my /etc/mail/client-info:

AuthInfo:*.comcast.net "U:root" "I:comcast_user" "P:comcast_password"

Now, I know everything is fine with the u/p, as I could authenticate directly through SMTP, using telnet.

There are two things I don't understand.

1. When AuthInfo records are searched for, they are matched by the target hostname. How? Does it it use the map key (something I would expect), or uses the so-called "Domain" ("R:" parameter that I don't set in my auth-info line)




2. What is "U:", really? Sendmail README (http://www.sendmail.org/m4/smtp_auth.html) says it's "user(authoraztion id)", and "I:" is "authentication ID". That suggests that my username should be in "U:", actually, but http://www.sendmail.org/~ca/email/auth.html says that "I:" is your remote user name.

The session looks like this:

[root@manticore]/etc/mail# sendmail -qf -v
Warning: Option: AuthMechanisms requires SASL support (-DSASL)

Running /var/spool/mqueue/p97CgcWq023273 (sequence 1 of 399)
my@email.com... Connecting to smtp.comcast.net. port 587 via relay...
220 omta19.westchester.pa.mail.comcast.net comcast ESMTP server ready

>>> EHLO my.host.name
250-omta19.westchester.pa.mail.comcast.net hello [my.ip.add.res], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 15728640
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-STARTTLS
250 OK
>>> STARTTLS

220 2.0.0 Ready to start TLS
>>> EHLO my.host.name
250-omta19.westchester.pa.mail.comcast.net hello [my.ip.add.res], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 15728640
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 OK
>>> MAIL From:<> SIZE=2183

550 5.1.0 Authentication required
MAILER-DAEMON... aliased to postmaster
postmaster... aliased to root
root... aliased to my@email.com
postmaster... aliased to root
root... aliased to my@email.com
>>> RSET
250 2.0.0 OK



[root@manticore]/etc/mail# sendmail -d0.1
Version 8.14.3
 Compiled with: DNSMAP LOG MAP_REGEX MATCHGECOS MILTER MIME7TO8 MIME8TO7
                NAMED_BIND NETINET NETINET6 NETUNIX NEWDB NIS PIPELINING SCANF
                SOCKETMAP STARTTLS TCPWRAPPERS USERDB XDEBUG

Thanks,
Pawel.