Situation

I want to unit test applications that send emails. Obviously I don’t want to be opening a dozen of real email accounts just to test this thing out. Naturally I would want to install an SMTP/POP3/IMAP server on Windows, and there is one free (open source) option that is quite promising – hMailServer. However, it still involves 2 (quite major) inconveniences for my use case:

• I have to go through the configuration screens to create new users. i.e. if I want to send email to alice@localhost I’d have to create the user account alice manually
• I have to use an email client (like Outlook Express) to connect to the local POP3 server to view the emails. This seems redundant to me, since the files are already stored in my disks, why can’t I just view them?

The Solution

Then I came across exim on cygwin. exim is (as it claims to be) a vast improvement over the good ol’ sendmail. So I gave it a shot – man, that was awesome! I can now direct my application to send to arbitrary address like alice@mail.local, foobar@mail.local and I can view the results immediately in a text file, solving the two problems mentioned above. Here’s what I did:

• Install exim using cygwin installer
• Run exim-config
• Edit /etc/exim.conf
• Uncomment primary_hostname and set it to mail.local
• Edit the router localuser, comment out the line check_local_user (If you don’t know what that means, just search for the line localuser:)
• Edit %WINDIR%\system32\drivers\etc\hosts, add the line

• Finally, reboot the exim service

And there you go! You can now send mail to *@mail.local. To view the mail, go to /var/spool/mail which contains all the mail in text files. A simple tail -f /var/spool/mail/foobar can monitor the mail sent to foobar@mail.local

A simple test to make sure everything’s working:

$ exim -bt foobar@mail.local
foobar@mail.local
  router = localuser, transport = local_delivery
# If something is wrong in your config, it would say "Unrouteable address"
 
# Now let's try sending an email
$ exim -v -odf foobar@mail.local
Hello World!
.
LOG: MAIN
  <= Chris@mail.local U=Chris P=local S=296
delivering KEQKED-0002RS-A7
LOG: MAIN
  => foobar <foobar@mail.local> R=localuser T=local_delivery
LOG: MAIN
  Completed
 
# Cool, let's see if it really delivered
$ tail /var/spool/mail/foobar
Received: from Chris by mail.local with local (Exim 4.69)
        (envelope-from <Chris@mail.local>)
        id KEQKED-0002RS-A7
        for foobar@mail.local; Sun, 08 Feb 2009 15:20:39 +0800
Message-Id: <EKEQKED-0002RS-A7@mail.local>
From: Chris <Chris@mail.local>
Date: Sun, 08 Feb 2009 15:20:39 +0800
 
Hello World