sendmail

Viewing email in Linux using postfix's mailq and postcat

When I'm developing using the Drupal Development VM, or checking into email processing on any of my servers, I usually use postfix to handle mail sending. Postfix is simple, preinstalled on most Linux distributions (and easy to set up if not), and is easy enough to use.

Here are the most common commands I use when either developing or troubleshooting email in production:

  • mailq - print a list of all queued mail
  • postcat -vq [message-id] - print a particular message, by ID (you can see the ID along in mailq's output)
  • postqueue -f - process the queued mail immediately
  • postsuper -d ALL - delete ALL queued mail (use with caution—but handy if you have a mail send going awry!)

There are many other helpful commands and scripts to help deal with mail (e.g. deleting all messages to a certain domain, or deleting specific message IDs easily), but these are the main ones I use during day-to-day development and troubleshooting.

Route local emails to another email address using Postfix on Linux

When I set up new servers, I like to make sure any system messages like cron failures, server issues, or emails that are routed to johndoe@example.com (where 'example.com' is the hostname of the server—meaning emails to that domain will get routed through the server itself and not hit an external MX server unless postfix/sendmail is configured correctly) are sent to my own email address.

It's relatively straightforward to route emails to internal users (like webmaster, root, etc.) to an external email address; you simply need to edit the /etc/aliases file, adding a rule like the one below, then run the command sudo newaliases:

webmaster: root

# Person who should get root's mail
root: youremail@example.com

By default, most internal users are routed to root as well (including webmaster), so setting an external email address (or a list of addresses, separated by comma) for the root account will allow you to more easily see what's happening on your server. Don't forget to run sudo newaliases to pick up the changes!

Configure sendmail on CentOS to allow sending of email from localhost

For some of my Drupal sites and PHP scripts (and shell scripts) that I run on a VPS I manage, I need to simply be able to send outgoing emails from arbitrary email addresses. I could go into all the details of DNS SPF records and MX records here, but that's something you'll need to research on your own. This post simply shows how to install and configure sendmail on a CentOS box to just allow outgoing mail from php's mail() function, the mail command line utility, etc., and only from localhost (127.0.0.1):

First, install sendmail with $ sudo yum install sendmail sendmail-cf.

Then, configure sendmail by editing the file /etc/mail/sendmail.mc (don't edit the sendmail.cf file - we'll auto-generate that after setting things correctly in sendmail.mc).

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