I'm trying to use the mail() function in PHP on a Debain Linux server.
I have 2 web servers running. One is in a chrooted setup.
The server that's not chrooted works fine, the other one wont send email.
Any idea how I can setup emailing in the chrooted setup?
There is a small utility called "mail" or "email" or something like that, which can be installed as a simple replacement for sendmail, postfix, qmail, ... Just install to the chrooted environment and redirect the mails to the mailserver outside the jail.
PHP uses the external sendmail program to send E-mail messages (1, 2). To avoid installing it in its entirety in the chroot jail, lightweight programs exist that can provide the necessary functionality within the jail. How-tos for setting this up exist.