[CentOS] sendmail - smtp security/authentication & port 587 issues

Greetings,

I'm refining a CentOs configuration installation, now just over one month 
old running on a colocated production server. Previously, we ran a version 
of Fedora for over seven years.

Specifically, I'm reviewing our sendmail configuration, both with respect 
to authentication and port usage.

Previously, we had the following line in the sendmail.mc line:
define(`confAUTH_MECHANISMS', `DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl

To authenticate, users would first have to POP their mail.

A klunky script would scan appropriate log files and copy relevant IP 
addresses to the /etc/mail/access file that would be regenerated every 
5 minutes via cron.

Once the IP address was in the /etc/mail/access.db a user could be 
authenticated and be allowed to send email using the machine as smtp.

Is there a better way of doing this?


Port 587 issues:
Verizon DSL filters out requests on port 25 to smtp servers not belonging 
to verizon.net. An alternative is to use port 587 for smtp purposes.

Are there any views in this CentOs user community on this?

Much thanks.

Max Pyziur
pyz at brama.com