I have a linux server and I keep getting a sendmail error "501 bad address syntax" and a "data format error". what does this error mean? usually if the email address is wrong or doesn't exist it will give me an "Undelivered Mail Returned to Sender" message. but this is different. if I try to send a mail message from within the sendmail from the commandline it sends fine. but when mail gets sent from a php script I get that "501 bad address syntax" error. it seems to me that the send mail server is configured correctly because I can send messages from sendmail directly. but when it is originating from a php script it fails. any ideas. maybe there's someone out there that is more familiar with sendmail than me.