I am not sure about the case of your problem, probably it is your configuration of squirrelmail...
Of course, i suppose that your system requirements to run Squirrelmail are correct.
Maybe this article helps you on the right track anyway:
Create a data directory and attachements directory.
In my example the names of these directories are: sqmdata & sqmattachements.
For security reasons, create them outsite your web for squirrelmail.
Creating these two directories in /var/www is a good idea.
Make these new directories writebable for Apache, you have to make the Squirrelmail data directory and attachements directory writeable for Apache.
In Debian you can do that with these commands:
chown -R www-data:www-data sqmdata
chown -R www-data:www-data sqmattachments
chmod 300 sqmdata
The names "www-data", might differ on other Linux distros.
Then startup the configuration program in de config directory of Squirrelmail with the command conf.pl
There you have to define the locations of the sqmdata and sqmattachments directories.
I refer to this documentation: http://www.squirrelmail.org/wiki/Cha...oryPermissions
An other possibility might be that the index.php file does not redirect correctly to your Squirrelmail login screen/site...
I hope this article helps you.
If not, maybe others can give you some support in this forum.