We used to use horde to provide our webmail service, but redhat now provides squirrelmail for this purpose. So, installed the package with up2date:
up2date squirrelmail
This also installed package: php-mbstring
Instructions are to restart httpd and go to http://
/usr/share/squirrelmail/config and run:
./conf.php
Then go through and change the settings to match our site. After changing everything, I was allowed to log in.