If Netscape just sits there when you are trying to send a mail message, maybe you should upgrade your version of Netscape. In the form for the compose screen, Squirrelmail uses ENCTYPE="multipart/form-data". This is in the HTML 4.01 specification, and should be supported by all browsers. However, some versions of Netscape are not standards compliant. You will need to edit the file "functions/compose.php" and remove that part. Doing this may break sending of attachments though. The best solution is to use another browser (Mozilla, Galeon, Lynx, Links, IE) or to upgrade Netscape.
If you have upload disabled in your php configuration, squirrelmail will not send email at all. You may be able to read email but sending email will not work. Check your php.ini file to make sure that you have allowed file uploading with php. Also note this issue is addressed in other places on this site, like here: MailDoesNotSend.
In my opinion enabling file upload is a security issue, you should consider disabling attached files and changing the multipart/formdata enctype.
Gabor Deri, firstname.lastname@example.org
Set file_uploads = On in /etc/php.ini .