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I've got several production servers running a LAMP stack. They each have a local Postfix server catching any mail from the system and from PHP, and relaying it via a smarthost (the SendGrid SMTP service).

I'd like to add a custom header to every outgoing message sent to the smarthost. This allows me to filter statistics per server in SendGrid. Something like:

X-SMTPAPI: {"category": "www1"}

The Postfix docs mention using the PREPEND action in a Postfix 'access' table. So, I added the following line to /etc/postfix/access:

PREPEND X-SMTPAPI: {"category": "www1"}

and hashed the access file with postmap.

However, I have no idea how to use the map. Something like the following doesn't work:

smtp_client_restrictions = check_client_access hash:/etc/postfix/access

How do I make Postfix prepend this header?

sysadmin1138
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Martijn Heemels
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3 Answers3

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This answers your exact question: https://web.archive.org/web/20150706131729/http://hoursofop.tumblr.com/post/17760274650

Quick steps reported here:

  • create a file /etc/postfix/sendgrid_headers and add this line to it:

    /^From:/ PREPEND X-SMTPAPI: {“category” : “Category Name”}

  • update your master.cf file with the following lines:

    smtp      unix  -       -       n       -       -       smtp -o smtp_header_checks=regexp:/etc/postfix/sendgrid_header

It applies to a Ubuntu system and worked perfectly for me. Be careful to choose the right "smtp" line in master.cf. I used a tab to indent the -o line.

Also note that SendGrid strips out the X-SMTPAPI header from the email before it is sent on - so you won't find it there but you will see the category appear within the SendGrid dashboard.

WiseOwl9000
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You seem to have mis-spelled header_checks as smtp_client_restrictions, which isn't even the correct spelling of the wrong parameter. ☺

This sort of thing is far better done with a simple shim around sendmail, that your PHP (or whatever) scripts are configured to use, you know. The shim script would be a simple exercise in the use of the cat and echo commands. The MTS is really the wrong place to be doing this.

AlexD
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JdeBP
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  • Couldn't get it working with header_checks either. Also, that processes every single header so appears to be overkill for such a simple task. Thanks for the suggestion of using a wrapper, but that also seems like a kludge for something an MTA should be able to do with ease. Is there really no 'easy' way? – Martijn Heemels Jun 17 '11 at 20:38
  • Yes, there's an easy way, and it's the way of the shim script. Concocting application-layer message content like this _is the job of the MUA_, not the MTS. This task is fully and squarely within the realm of PHP and the agents that it uses to concoct messages before submission, not in the MTS. – JdeBP Jun 18 '11 at 10:03
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I had a similar problem with Sparkpost: I needed to add their custom header in order to set some delivery options.

This problem (adding a custom header to all emails) has many different solutions.

My solution is using Postfix header_checks and prepending the custom header to the "From" header.

  • Create a new file, named /etc/postfix/my_custom_header:

    /^From:/i X-MSYS-API: { "options" : {"transactional": true} }

  • Edit /etc/postfix/main.cf (appending to the bottom):

    # Add custom Sparkpost X-MSYS-API header to all mails
header_checks = regexp:/etc/postfix/my_custom_header

  • reload Postfix configuration (this command is for Debian Wheezy, and may be different on your OS)

    service postfix reload

EDIT: Unfortunately, this method adds the header to all emails (incoming and outgoing). I am still searching for a method that adds the header only to outbound emails.

gog
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