Mail Server: Rewriting Addresses to Handle One Envelope Recipient Spam
Email spam has been a persistent issue for many years, with spammers constantly finding new ways to bypass filters and deliver unwanted messages to users. One technique that spammers use is to send a single email to multiple recipients using the same envelope, but with different recipient addresses in the message headers. This can cause problems for mail servers, as they may not be able to correctly identify and filter out spam messages.
The Problem with Single Envelope Recipients
When a mail server receives a message with a single envelope containing multiple recipient addresses, it may not be able to correctly identify and filter out spam messages. This is because the spam filter is only able to examine the envelope recipient, and not the individual recipient addresses in the message headers. As a result, spam messages may be delivered to valid recipients, causing frustration and reducing the effectiveness of the spam filter.
Rewriting Addresses to Handle Single Envelope Recipients
One solution to this problem is to rewrite the recipient addresses in the message headers to match the envelope recipient. This can be done using a mail server script or plugin, and will ensure that the spam filter is able to correctly identify and filter out spam messages. This technique is known as recipient address rewriting.
Example of Recipient Address Rewriting
Here is an example of how recipient address rewriting works:
Original message:To:Envelope recipient:[email protected]Rewritten message:To:
In this example, the recipient addresses in the message headers have been rewritten to match the envelope recipient ([email protected]). This ensures that the spam filter is able to correctly identify and filter out the spam message.
Implementing Recipient Address Rewriting
Recipient address rewriting can be implemented using a mail server script or plugin. The exact method will depend on the mail server software being used, but the general process is as follows:
- Identify messages with a single envelope containing multiple recipient addresses
- Rewrite the recipient addresses in the message headers to match the envelope recipient
- Deliver the message to the rewritten recipient addresses
Example Implementation using Postfix
Here is an example of how to implement recipient address rewriting using the Postfix mail server software:
- Create a new Postfix script called
rewrite-recipients.pl - Add the following code to the script:
#!/usr/bin/perl
use strict;
use warnings;
# Get the original message
my $original\_message = $ARGV[0];
# Get the envelope recipient
my $envelope\_recipient = $ARGV[1];
# Rewrite the recipient addresses in the message headers
$original\_message =~ s/To: .*?
/To: $envelope\_recipient
/g;
# Print the rewritten message
print $original\_message;
- Make the script executable by running the following command:
chmod +x rewrite-recipients.pl
- Add the following line to the Postfix
master.cffile:
rewrite-recipients unix n n - - pipe
flags= user=vmail argv=/path/to/rewrite-recipients.pl ${sender} ${recipient}
This will tell Postfix to run the rewrite-recipients.pl script whenever a message is received with a single envelope containing multiple recipient addresses. The script will rewrite the recipient addresses in the message headers to match the envelope recipient, and the message will be delivered to the rewritten recipient addresses.
Recipient address rewriting is a powerful technique for handling spam messages with a single envelope containing multiple recipient addresses. By rewriting the recipient addresses in the message headers to match the envelope recipient, the spam filter is able to correctly identify and filter out spam messages. This ensures that valid recipients do not receive unwanted messages, and improves the overall effectiveness of the spam filter.
References
- Postfix: http://www.postfix.org/
- Recipient Address Rewriting: https://www.mail-archive.com/[email protected]/msg15866.html