All of the DNS blacklists we used a couple years ago are defunct. There are, however, a slew of new DNS-based blacklists that can help protect your users from spam. Understand that with any blacklist there is a chance that legitimate email will be blocked. Balancing this against the cost and annoyance of spam is […]

If you have bad messages in your Postfix mail queue, you can list them with the postqueue command: [root@svr-1 mail]# postqueue -p -Queue ID- –Size– —-Arrival Time—- -Sender/Recipient——- 4C63F2300BA 876 Mon Jun 5 09:31:54 user@somedomainsomewhere.com (connect to example.com[192.0.34.166]: Connection timed out) differentuser@example.com — 1 Kbytes in 1 Request. You will need the Queue Id to […]

Make sure that you are not running an old version of formmail.pl. Check your cgi-bin directory to make sure. Even though the fix for formmail has been out since last August, we are still getting scanned for this on our webservers. Old versions of formmail.pl can be used to send spam. For more info, check […]

Postfix has the ability to reject mail based on regular expression matching in the header of the incoming mail message. To enable this, add these lines to main.cf: header_checks = regexp:/etc/postfix/header_checks header_checks = pcre:/etc/postfix/header_checks We stuck these after the alias line. Add the header content matches and actions to header_checks (usually in /etc/postfix) and restart […]

If you are using an email client besides Outlook (gasp!), you have most likely run into the attachment winmail.dat. Supposedly this can be prevented on the client side by sending mail in plain text; however, this doesn’t appear to work with attachments. We ran across a cool utility at Fentun that will extract attachments out […]

When migrating from an internal email system to Google Apps, it’s nice to have the option of running a pilot program including a few of your users to try it out, and then to move the rest of the users over when problems with the transition have been identified and addressed. This is pretty easy […]

As systems administrators, we abhor spam. It bogs down servers, floods our personal mailboxes, and wastes our user’s time. As web content providers, we also are extremely annoyed that email contact information is blatently reaped and abused. The Internet can be so much more than a cesspool of spam. On the other hand, the Internet […]

As you may or may not know, Washington State has a spam law that forbids deceptive email practices. For more info on this law see this area of the Attorney General of Washington’s website. Well, a landmark case regarding this law has just been decided. We put a copy of the release up on NetAdminTools […]

One good trick to use when testing your email server is to use telnet. To send email, you can just telnet into the destination email server directly: u-1@srv-1 u-1 $ telnet yourmailserver.com 25 Trying 21.40.23.46… Connected to yourmailserver.com. Escape character is ‘^]’. 220 mx.yourmailserver.com ESMTP Sendmail 8.12.9/8.12.9; Thu, 12 Jun 2003 10:06:19 -0700 helo frommail.com […]

Due to DDoS attacks on Osirusoft, Osirusoft decided to reject all. So, if you are using Osirusoft to block spam, stop! Well, hats off to the valiant efforts of Osirusoft. Can’t really blame them for their reaction to this world of shit. The beautiful thing is that sysadmins and others in our community will find […]

It is truly amazing how many resources are taken up on a server by other rogue boxes searching for an open relay, or simply sending dictionary attempts at finding local users. Watch-maillog is a perl script that uses IPtables to block mail servers that abuse your server. Watch-maillog helps with this by blocking servers that […]

We often need to mail brief messages from servers to send config files, or quick messages to other sysadmins. Pine works well for this, and the installation is mostly a single binary. We usually are logged in on some account that isn’t the email address we wish replies to come to. It turns out that […]

If you simply want to make a mailbox receive mail for another address, just add the full address to /etc/postfix/virtual: [root@srv-2 postfix]# cat virtual usr-1@networking.com usr usr-1@networking2.com usr usr-2@maildomain.com anotherusr If we simply add this line to the bottom: usr-3@maildomain.com anotherusr Mail that was was delivered previously via usr-2@maildomain.com will be delivered in the same […]

The MIME on Outlook Express seems to be broken. We have seen several instances where Outlook Express users cannot read Email sent by UNIX Email clients. The message is garbled with lots of question marks and other random characters. We have had this problem here at netadmintools.com, since we use Linux Office Suite 99 for […]

Spiderkiller is a C program that will generate unique pages with random email addresses that will confuse harvesting bots. Compile the app: srv-5:~ usr4$ gcc spiderkiller.c -o spiderkiller spiderkiller.c: In function ‘main’: spiderkiller.c:299: warning: incompatible implicit declaration of built-in function ‘strlen’ The options are simple: srv-5:~ usr4$ ./spiderkiller -help Usage: spiderkiller [-help] [-n ] [-k […]