[EN] Email flow modifier

We have developed a technology that we have called “Email flow modifier“. Some people have interest on this subject, we will expose a technical text about how we have implemented it.

Why email flow modifier ?

This system allows us to develop rate of reply and response time. It is important to us to recollect statistical information about email contact between owners and users, because this is the critical section in our business.

It also allows us to prevent “spammer behavior“. You may have a web form in whitch you want to allow contact between a user ([email protected]) and a service ([email protected]). Then, from yourdomain.com you are sending an email to [email protected] from [email protected]. Implementing the email flow modifier, all emails are sent as [email protected]. So you are not having any more the “spammer behavior”.

General system view

Phase 0: User is writing at service-[code]@yourdomain.com on first time, using sender [email protected]. (Email address service-[code]@yourdomain.com and context can be generated using a web form).

Between phase 0 to 1, on the email server:
A code for this user referring to that service is generated (user-[code]@yourdomain.com).

Phase 1: The service gets a new email from user-[code]@yourdomain.com.

Phase 2: The service replies to the user using the user-[code]@yourdomain.com email.

Between phase 2 to 3, on the email server
The email adreess has user-[code]@yourdomain.com format. From this code, we can get the real address [email protected] and the recipient address service-[code]@yourdomain.com.

Phase 3: The original From and To are changed, and this new email is sent. The users receives a new email from service-[code]@yourdomain.com.

Phase 4: Is is basically identical to Phase 0, but now we already know the user code, so we do not need to create a new one.

Email server requisites

It is likely that the system we implemented can be done on another email server. Basic requirements:

• Email address using wildcards must be supported.
• You need to be able to execute a script in order to manage the email. (qmail it is really flexible on this aspect).

Implementation

The hardest part on this project is to get the theoretical part working. The script will be as complex as additional functionalities are being implemented. The programming language we choose is Perl, but you can do the same in several others.

First, we need to create wildcards email accounts. We are using qmail, so the way to do it is creating two files, .qmail-user-default and .qmail-service-default. The content on these files will be the same:

|/path/to/script/emailflowmodifier.pl

So, when a new email is sent the script will take care of it.

Then, in our script, we read the entire email:

while ($mail=<STDIN>) {
    $completeemail .= $mail;
}

Then we split the headers from the body, and we modify the headers so each header will be on one line.

@tempmail = split(/\n\n/, $completeemail, 2);
$header = @tempmail[0];
$header =~ s/\n\s+/ /g;

Then we create an associative array with email headers (name/value)

%hdrs   =  (UNIX_FROM => split /^(\S*?):\s*/m, $header);

$command = "/var/qmail/bin/qmail-inject < /tmp/newmail.tmp";
$res = `$command`;