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Questions[spam](server)

Martin Hope
Stefan Seidel
Asked: 2016-04-22 10:15:57 +0800 CST
  • 42

I operate a small mail server for my private emails, some friends who have websites and two NGOs. In total my server sends between 60 and 400 messages a day. Now a lot of these emails are personal mails, between two or more people who know each other. Occasionally (usually once or twice a week) there will be a mailing that goes out to "members" of one NGO, informing them what's new etc.

Now I have already moved off the "mass mailings" (about 100 recipients, all personally known and manually subscribed through a paper form) to mailgun.org.

I still get (and increasingly so), rejected messages. Especially big email providers like Gmail, Yahoo or Microsoft (hotmail, live.com, ...) just decide to reject with a 550 or send personal messages to the Spam folder of the recipients. Sometimes this happens:

  • gmail user sends email to user on my system
  • user on my system replies
  • the reply is being rejected or sent to spam

Things I have done:

  • set up DKIM (per-domain signing of all outgoing email)
  • set up SPF, domains usually have ~all, some -all
  • I have a correct PTR for my mail server IP
  • obviously no open relay, users can only send from their own email address after authentication
  • I have DMARC policies for most of the domains
  • I rate limit outgoing messages, for some mail servers down to 1 per minute
  • mail test services report "perfect" scores (all pass) for all of the above
  • I regularily check my IP for blacklisting using http://www.dnsbl.info - it's always all green

Now the paradox comes here: for most of the big mail providers, there is a way to register to monitor rejection rates and IP reputation:

but I do not classify as bulk sender, because of the low volume. So I did register to monitor my reputation and rejection rates, but because I do not send bulk email, there are no reports.

Is there anything else I can do to improve mail delivery rates? Or should I give in and stop trying to operate my own mail server?

In case it is relevant: I use postfix and have very strict rules about incoming mail (i.e. no unknown domains/host names or invalid SPF records, I use spamassassin etc.)

Update

Here is an example, sent from me to my in-laws and it arrived in their SPAM folder: http://pastebin.com/BC6YgjpQ (I replaced the sending address domain with example.com and the receivers address with [email protected])

Since the question came up: Connections to Gmail are Untrusted TLS connection established to gmail-smtp-in.l.google.com[2a00:1450:400c:c0b::1b]:25: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits) encrypted.

email spam email-server spf dkim
Martin Hope
Chris S
Asked: 2012-08-21 12:30:19 +0800 CST
  • 110

This is a Canonical Question about Fighting Spam.
Also related:

There are so many techniques and so much to know about fighting SPAM. What widely used techniques and technologies are available to Administrator, Domain Owners, and End Users to help keep the junk out of our inboxes?

We're looking for an answer that covers different tech from various angles. The accepted answer should include a variety of technologies (eg SPF/SenderID, DomainKeys/DKIM, Graylisting, DNS RBLs, Reputation Services, Filtering Software [SpamAssassin, etc]); best practices (eg mail on Port 25 should never be allowed to relay, Port 587 should be used; etc), terminology (eg, Open Relay, Backscatter, MSA/MTA/MUA, Spam/Ham), and possibly other techniques.

email spam spf dkim
Martin Hope
Billy Moon
Asked: 2012-08-09 06:17:34 +0800 CST
  • 111

I receive Mailer Daemon messages saying certain emails fail. My domain is itaccess.org which is administered by Google apps. Is there any way I can identify who is sending emails from my domain, and how they are doing it without me creating an account for them?

Delivered-To: [email protected]
Received: by 10.142.152.34 with SMTP id z34csp12042wfd;
        Wed, 8 Aug 2012 07:12:46 -0700 (PDT)
Received: by 10.152.112.34 with SMTP id in2mr18229790lab.6.1344435165782;
        Wed, 08 Aug 2012 07:12:45 -0700 (PDT)
Return-Path: <[email protected]>
Received: from smtp-gw.fsdata.se (smtp-gw.fsdata.se. [195.35.82.145])
        by mx.google.com with ESMTP id b9si24888989lbg.77.2012.08.08.07.12.44;
        Wed, 08 Aug 2012 07:12:45 -0700 (PDT)
Received-SPF: neutral (google.com: 195.35.82.145 is neither permitted nor denied by best guess record for domain of [email protected]) client-ip=195.35.82.145;
Authentication-Results: mx.google.com; spf=neutral (google.com: 195.35.82.145 is neither permitted nor denied by best guess record for domain of [email protected]) [email protected]
Received: from www20.aname.net (www20.aname.net [89.221.250.20])
    by smtp-gw.fsdata.se (8.14.3/8.13.8) with ESMTP id q78EChia020085
    for <[email protected]>; Wed, 8 Aug 2012 16:12:43 +0200
Received: from www20.aname.net (localhost [127.0.0.1])
    by www20.aname.net (8.14.3/8.14.3) with ESMTP id q78ECgQ1013882
    for <[email protected]>; Wed, 8 Aug 2012 16:12:42 +0200
Received: (from whao@localhost)
    by www20.aname.net (8.14.3/8.12.0/Submit) id q78ECgKn013879;
    Wed, 8 Aug 2012 16:12:42 +0200
Date: Wed, 8 Aug 2012 16:12:42 +0200
Message-Id: <[email protected]>
To: [email protected]
References: <20120808171231.CAC5128A79D815BC08430@USER-PC>
In-Reply-To: <20120808171231.CAC5128A79D815BC08430@USER-PC>
X-Loop: [email protected]
From: [email protected]
Subject: whao.se:  kontot avstängt - account closed
X-FS-SpamAssassinScore: 1.8
X-FS-SpamAssassinRules: ALL_TRUSTED,DCC_CHECK,FRT_CONTACT,SUBJECT_NEEDS_ENCODING

    Detta är ett automatiskt svar från F S Data - http://www.fsdata.se

    Kontot för domänen whao.se är tillsvidare avstängt.
    För mer information, kontakta [email protected]

    Mvh,
    /F S Data

    -----

  This is an automatic reply from F S Data - http://www.fsdata.se

  The domain account "whao.se" is closed.
  For further information, please contact [email protected]

  Best regards,
  /F S Data
spam
Martin Hope
Saif Bechan
Asked: 2010-03-24 21:33:49 +0800 CST
  • 82

I have a server with apache and I recently installed mod_security2 because I get attacked a lot by this:

My apache version is apache v2.2.3 and I use mod_security2.c

This were the entries from the error log:

[Wed Mar 24 02:35:41 2010] [error] 
[client 88.191.109.38] client sent HTTP/1.1 request without hostname 
(see RFC2616 section 14.23): /w00tw00t.at.ISC.SANS.DFind:)

[Wed Mar 24 02:47:31 2010] [error] 
[client 202.75.211.90] client sent HTTP/1.1 request without hostname 
(see RFC2616 section 14.23): /w00tw00t.at.ISC.SANS.DFind:)

[Wed Mar 24 02:47:49 2010] [error]
[client 95.228.153.177] client sent HTTP/1.1 request without hostname
(see RFC2616 section 14.23): /w00tw00t.at.ISC.SANS.DFind:)

[Wed Mar 24 02:48:03 2010] [error] 
[client 88.191.109.38] client sent HTTP/1.1 request without hostname
(see RFC2616 section 14.23): /w00tw00t.at.ISC.SANS.DFind:)

Here are the errors from the access_log:

202.75.211.90 - - 
[29/Mar/2010:10:43:15 +0200] 
"GET /w00tw00t.at.ISC.SANS.DFind:) HTTP/1.1" 400 392 "-" "-"
211.155.228.169 - - 
[29/Mar/2010:11:40:41 +0200] 
"GET /w00tw00t.at.ISC.SANS.DFind:) HTTP/1.1" 400 392 "-" "-"
211.155.228.169 - - 
[29/Mar/2010:12:37:19 +0200] 
"GET /w00tw00t.at.ISC.SANS.DFind:) HTTP/1.1" 400 392 "-" "-"

I tried configuring mod_security2 like this:

SecFilterSelective REQUEST_URI "w00tw00t\.at\.ISC\.SANS\.DFind"
SecFilterSelective REQUEST_URI "\w00tw00t\.at\.ISC\.SANS"
SecFilterSelective REQUEST_URI "w00tw00t\.at\.ISC\.SANS"
SecFilterSelective REQUEST_URI "w00tw00t\.at\.ISC\.SANS\.DFind:"
SecFilterSelective REQUEST_URI "w00tw00t\.at\.ISC\.SANS\.DFind:\)"

The thing in mod_security2 is that SecFilterSelective can not be used, it gives me errors. Instead I use a rule like this:

SecRule REQUEST_URI "w00tw00t\.at\.ISC\.SANS\.DFind"
SecRule REQUEST_URI "\w00tw00t\.at\.ISC\.SANS"
SecRule REQUEST_URI "w00tw00t\.at\.ISC\.SANS"
SecRule REQUEST_URI "w00tw00t\.at\.ISC\.SANS\.DFind:"
SecRule REQUEST_URI "w00tw00t\.at\.ISC\.SANS\.DFind:\)"

Even this does not work. I don't know what to do anymore. Anyone have any advice?

Update 1

I see that nobody can solve this problem using mod_security. So far using ip-tables seems like the best option to do this but I think the file will become extremely large because the ip changes serveral times a day.

I came up with 2 other solutions, can someone comment on them on being good or not.

  1. The first solution that comes to my mind is excluding these attacks from my apache error logs. This will make is easier for me to spot other urgent errors as they occur and don't have to spit trough a long log.

  2. The second option is better i think, and that is blocking hosts that are not sent in the correct way. In this example the w00tw00t attack is send without hostname, so i think i can block the hosts that are not in the correct form.

Update 2

After going trough the answers I came to the following conclusions.

  1. To have custom logging for apache will consume some unnecessary recourses, and if there really is a problem you probably will want to look at the full log without anything missing.

  2. It is better to just ignore the hits and concentrate on a better way of analyzing your error logs. Using filters for your logs a good approach for this.

Final thoughts on the subject

The attack mentioned above will not reach your machine if you at least have an up to date system so there are basically no worries.

It can be hard to filter out all the bogus attacks from the real ones after a while, because both the error logs and access logs get extremely large.

Preventing this from happening in any way will cost you resources and it is a good practice not to waste your resources on unimportant stuff.

The solution i use now is Linux logwatch. It sends me summaries of the logs and they are filtered and grouped. This way you can easily separate the important from the unimportant.

Thank you all for the help, and I hope this post can be helpful to someone else too.

apache-2.2 security spam
Martin Hope
kcode
Asked: 2009-07-31 21:53:20 +0800 CST
  • 96

This is a canonical question about how to handle email sent from your server being misclassified as spam. For additional information you may find these similar questions helpful:

Sometimes I want to send newsletters to my customers. The problem is, that some of the emails get caught as spam messages. Mostly by Outlook at the client (even in my own Outlook 2007).

Now I want to know what should be done to create "good" emails. I know about reverse lookup etc., but (for example), what about a unsubscribe link with an unique ID? Does that increase a spam rating?

email spam spam-filter