Squirrelmail and Roudcubemail

Hi,

I always used squirrelmail.

My squirrelmail.conf is:

Alias /webmail /usr/share/squirrelmail

 <directory "="" usr="" share="" squirrelmail="" plugins="" squirrelspell="" modules"="">Deny from all</directory> 

# this section makes squirrelmail use https connections only, for this you
# need to have mod_ssl installed. If you want to use unsecure http
# connections, just remove this section:
 <directory usr="" share="" squirrelmail="">RewriteEngine  on
  RewriteCond    %{HTTPS} !=on
  RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}</directory> 

This makes squirrelmail accessible from https://mydomain/webmail

Now I installed roundcube mail and I want to access squirrelmail from

https://mydomain/squirrelmail

and roundcube from

https://mydomain/roundcube

I noticed that if I set the alias

Alias /webmail /usr/share/squirrelmail

or

Alias /webmail /usr/share/roundcube

I can access roundcube and squirrelmail without problem.

If I set this alias

Alias /squirrelmail /usr/share/squirrelmail

and this

Alias /roundcube /usr/share/roundcube

I can't access any webmail.

It seems that the only alias that works ok on my system is /webmail

how this can be possible??