They aren't documented because we don't add them. Your PHP is either patched 
locally to do this, something else is adding it, or you have userspace code doing 
it.

The only header PHP optionally adds (disabled by default) is X-PHP-Originating-
Script which is documented here:

http://www.php.net/manual/en/mail.configuration.php

> They aren't documented because we don't add them. 
> Your PHP is either patched locally to do this, something else is adding it,
> or you have userspace code doing it.

Thanks for your explanation - this makes sense from PHP's perspective, but it's now really weird. Googling for these headers shows they are very widespread. I know there is no userspace code of mine doing this, and I don't think sendmail could be doing it (the MTA can't have knowledge of the HTTP user-agent).

I'm using the stock PHP build provided by Mageia.

You're right - sorry for wasting your time - this is a patch in the most unlikely place. Mandriva (and thence Mageia) have patched the source, in file php-mail.diff; here are the relevant lines.


+		if (PG(http_globals)[TRACK_VARS_SERVER]) {
+			zval **remote_addr, **server_name, **server_port,
+				**script_name, **http_user_agent;
+			
+			if (zend_hash_find(PG(http_globals)[TRACK_VARS_SERVER]->value.ht, "REMOTE_ADDR", sizeof("REMOTE_ADDR"), (void **) &remote_addr)==SUCCESS) {
+				convert_to_string_ex(remote_addr);
+				fprintf(sendmail, "HTTP-Posting-Client: %s\n", Z_STRVAL_PP(remote_addr));
+			}
+			if (zend_hash_find(PG(http_globals)[TRACK_VARS_SERVER]->value.ht, "SERVER_NAME", sizeof("SERVER_NAME"), (void **) &server_name)==SUCCESS) {
+				convert_to_string_ex(server_name);
+				fprintf(sendmail, "HTTP-Posting-URI: %s", Z_STRVAL_PP(server_name));
+				if (zend_hash_find(PG(http_globals)[TRACK_VARS_SERVER]->value.ht, "SERVER_PORT", sizeof("SERVER_PORT"), (void **) &server_port)==SUCCESS) {
+					convert_to_string_ex(server_port);
+					fprintf(sendmail, ":%s", Z_STRVAL_PP(server_port));
+				}	
+				if (zend_hash_find(PG(http_globals)[TRACK_VARS_SERVER]->value.ht, "SCRIPT_NAME", sizeof("SCRIPT_NAME"), (void **) &script_name)==SUCCESS) {
+					convert_to_string_ex(script_name);
+					fprintf(sendmail, "%s", Z_STRVAL_PP(script_name));
+				}
+				fprintf(sendmail, "\n");
+			}
+			if (zend_hash_find(PG(http_globals)[TRACK_VARS_SERVER]->value.ht, "HTTP_USER_AGENT", sizeof("HTTP_USER_AGENT"), (void **) &http_user_agent)==SUCCESS) {
+				convert_to_string_ex(http_user_agent);
+					fprintf(sendmail, "HTTP-Posting-User-Agent: %s\n", Z_STRVAL_PP(http_user_agent));
+			}
+		}


[I'll add a pointer to this bug report into the mail() user-docs, so that other people can at least find this more easily.]

And no way to turn it off. Not a very friendly patch.

Crossref: I've filed this for Mageia. 
https://bugs.mageia.org/show_bug.cgi?id=4571

The specfile credits PLD for the original patch.

I saw you mentioned it should be implemented upstream. For spam-detection 
purposes, I don't think all those headers are all that useful. What you really 
want to know, as an ISP, is which script on your server is being used to send 
spam with. The IP and user-agent isn't all that useful and if you really want 
those, you can dig them out of your access logs since you know which script was 
hit. We already have that capability implemented via mail.add_x_header.

I agree - this feature isn't very useful, even upstream.

I have found an ugly workaround: Postfix supports checking (and removing) headers. (There is probably a similar fix for all other MTAs)

1. Enable header-checks, in /etc/postfix/main.cf :
    header_checks = regexp:/etc/postfix/header_checks

2. Specify the headers to strip, in /etc/postfix/header_checks :

/^HTTP-Posting-Client:/      	IGNORE
/^HTTP-Posting-URI:/     	IGNORE
/^HTTP-Posting-User-Agent:/     IGNORE