LinuxQuestions.org - sendmail 8.13.4-2 smtp auth nightmare

I am running FC4 with the sendmail version above.
Recently my ISP started requiring SMTP authentication on all outgoing mail.
I would have no problem with that - however sendmail doesn't seem to like my smtp auth configuration.

Here's what I did first:
1. I created a file called default-auth-info in my /etc/mail directory.
The contents of it are as follows:

Code:

AuthInfo:mail.my.isp "U:username" "P: :) " "M:LOGIN"

Then I did

Code:

makemap hash default-auth-info < default-auth-info

2. Next I made some changes to sendmail.mc.
I added the following:

Code:

FEATURE(`authinfo',`hash /etc/mail/default-auth-info')dnl

Then I uncommented these lines:

Code:

TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl

define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl

3. I then did a make on the mc file to get sendmail.cf.
4. I restarted the sendmail server.

Then I tried to send an email. It was NOT received.
I checked the log file.

Code:

Oct 29 21:27:13 localhost sendmail[13652]: j9TMDs8E010600: to=<me@somewhere.com>, ctladdr=<me@localhost.localdomain> (501/501), delay=03:13:19, xdelay=00:00:01, mailer=relay, pri=1200365, relay=mail.my.isp. [131.183.2.205], dsn=4.0.0, stat=Deferred: 454 5.7.3 Client does not have permission to Send As this sender.

What could be the problem? Could someone explain to me also the difference between U and I in the authinfo file?