To secure squirrelmail, edit the following file and edit it to look like below.
vi /etc/httpd/conf.d/squirrelmail.conf
Alias /webmail /usr/share/squirrelmail
<Directory “/usr/share/squirrelmail”>
SSLRequireSSL
Options Indexes MultiViews
AllowOverride None
Order deny,allow
Deny from all
Allow from all
</Directory>
Thats it.
NB: Remember now the only way to access mail is by https://……../webmail not http://……/webmail otherwise you get a nice page saying Forbidden!