imap_mail problems

Hello, I am having problems with this code below. The system is a FC1 server and it is supposed to send an email collecting some information of a computer. The problem I am having is with the "<" and ">" characters. When the $header variable is created, it does not work if you add the < and > characters. For some reason makes the whole string like null. Has anyone seen this behaviour? If I try manually to send an email it does work and php does have imap support on it. Thanks -pa <snip> $header = "From: $fullNameField <admin@" . trim(/bin/hostname --fqdn) . ">"; $registrationAddress = "myname@mydomain.com"; $subject = "Registration ($productName)"; $message = " Full name: $fullNameField Title: $titleField Company: $companyField "; // send email imap_mail($registrationAddress, $subject, $message, $header); <snip> -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.