LinuxQuestions.org
Visit the LQ Articles and Editorials section
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Security
User Name
Password
Linux - Security This forum is for all security related questions.
Questions, tips, system compromises, firewalls, etc. are all included here.

Notices

Reply
 
Search this Thread
Old 08-03-2010, 08:45 AM   #1
elmucis
LQ Newbie
 
Registered: Jul 2010
Posts: 1

Rep: Reputation: 0
Sendmail - fight against the spammers


I am new to Slackware and sendmail.

1) I want to make sendmail more resist from spammers. Can You suggest some lines in sendmail.mc (My server is iauto.lv) Can I do, that my server recieves mails, but users cannot send mails with SMTP through my server?


2) Many mailservers returned mails, because I have no reverse DNS. What I must to do?

Last edited by XavierP; 08-03-2010 at 11:28 AM. Reason: Moved to Security
 
Old 08-04-2010, 05:28 PM   #2
Noway2
Senior Member
 
Registered: Jul 2007
Distribution: Ubuntu 10.10, Slackware 64-current
Posts: 2,124

Rep: Reputation: 776Reputation: 776Reputation: 776Reputation: 776Reputation: 776Reputation: 776Reputation: 776
Elmucis, Welcome to Linuxquestions.org.

In general terms you will want to make sure that your email (smtp) server is NOT what is called an open relay. An open relay will accept mail from (any) non-authenticated domain and forward it to the next hop. As you know, spammers typically look for open relays to work through. You will want to configure your server to use authentication. It appears that sendmail uses two methods for this: SMTP AUTH and Cyrus SASL. I am not familiar enough with sendmail (I use postfix) to tell you specifically how to do this, but you should consult the documentation and the how - to documents.

With respect to your other comment, it sounds like you are trying to run an email server via a dynamic IP address. As a general rule, mail from dynamic IP address blocks will be rejected as > 99.999% of it is spam from a hiacked machine. If you are running your server from a PUBLICLY static IP address (not static on your LAN), then you may need to add what is called an SPF record. An SPF record is a DNS function that allows a receiving MTA to do a reverse lookup and verify that your system is declared as being a mail sending agent. Obviously a system that has been hijacked by malware and is sending spam will not have an SPF record.
 
  


Reply

Tags
sendmail


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sendmail accepting spammers for local users jstrope Linux - Server 3 07-03-2008 09:59 AM
Spammers using my sendmail to send thier junk, need help please! cereal83 Linux - Security 14 02-22-2007 04:10 PM
LXer: A fight against evil or a fight for attention? LXer Syndicated Linux News 4 09-29-2006 08:05 AM
Very mad with spammers zidane2010 General 13 05-26-2004 01:57 PM
Spammers... Artimus LQ Suggestions & Feedback 10 03-18-2003 04:24 PM


All times are GMT -5. The time now is 05:46 PM.

Main Menu
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
identi.ca: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration