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sendmail and qmail both run on the same server. How can I know the one used to send email ?

I have a PHP application that sends email via the mail() function. The SMTP server it uses has both process running. It is a server used for live applications, so I can't stop one process to do some tests.

Thanks Cedric

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I'd make sure that the machine really is as you describe. It's possible to get confused about these things, especially as most Unix/Linux MTSes have a sendmail program image file that is nothing whatsoever to do with the Sendmail software package. There's almost never a need to set up a system in this way with two different MTS softwares running in parallel. (Multiple instances of one package is as exotic a configuration as things normally get.) –  JdeBP Jun 18 '11 at 12:45
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You will have to look in your php.ini file, under [mail function]. Here, the path to the mail sending binary is specified. Whatever is specified here, the mail() function in PHP will use.

sendmail_path = /usr/sbin/sendmail -t -i

The above one should be the default. So, if you haven't changed anything, PHP will use sendmail.

As @JdeBP mentions, you can also take a quick look at the headers of the mails received. If you look under the various Received sections, you will find some identification of the server software being used.

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Some systems have sendmail as a symlink to the actual binary provided by the MTA, e.g. sendmail.sendmail or sendmail.qmail. –  Ignacio Vazquez-Abrams Jun 17 '11 at 12:25
Oh, okay. Yeah, I'd trace down that one. Like your option though. –  slhck Jun 17 '11 at 12:28
+1. The suggestion in the PHP manual is to point sendmail_path directly at qmail_inject, which will be directly indicative with no further research. But in the general case finding out whose binary sendmail_path is pointing to is the right answer for PHP on Unix/Linux. –  JdeBP Jun 18 '11 at 12:40
While you're at it, you could mention in your answer that the Received: header fields in the received messages will yield very strong clues as to which software, Sendmail or qmail, processed the mail. Sendmail and qmail write trace information in different forms. –  JdeBP Jun 18 '11 at 12:50
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