Category Archives: EMail

Protecting domains from spammers

Spammers quite often ‘spoof’, or fake, the from address of an email.

As a result of this, many unsuspecting domain owners are being ‘blamed’ for spam that appears to come from their domain.

Fortunately, there is a relatively easy way to protect your domain from this: Publish DMARC policies.

If you are publishing SPF records and signing your email with DKIM, you can publish DMARC policies that tell receiving mail servers what do with emails that don’t align with the SPF and DKIM information.

SPF policies are DNS records that indicate what mail servers your mail is sent from.

DKIM is a way to add digital signatures to your email so that receiving mail servers can verify it was sent from an authorized source and that it wasn’t modified in transit.

Now what if you have a domain that you NEVER send email from?

Protecting those domains from being used in spam is even easier.

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Yahoo SMTP Deferrals Take 2

Well, our good friends at Yahoo are at it again.

Once again they are deferring mail for no apparent reason.

Nothing has changed on my system and yet they haven’t accepted a message to deliver to one of their users in 3 days (maybe more).  And, of course, there’s no way to actually contact a human to find out what is going wrong.

I’m on Yahoo’s email feedback loop … so I’m notified when someone complains about a message.  Nothing has come in recently from the feedback loop.

I used to be on their bulk sender white-list.  There was never a mention of having to renew the white-list approval.

A note to all my friends … DO NOT USE YAHOO FOR EMAIL!  Especially for business email.  The folks at Yahoo do NOT know how to provide service.

Gmail doesn’t have this problem … nor does Hotmail (much as I love to hate Microsoft).

Oh, and FWIW, yahoo customer service tends to ignore questions that are too complex for their script reading drones to answer.

Tech Tip: Don’t use qmail as a mail server

A while ago I added a new anti-spam technique to my mail server setup called “No Listing”.

No listing basically means putting a high priority MX record in the DNS that always rejects mail server connections..

It seems, however, that the qmail mail server can’t cope with that.  It’s not RFC compliant.

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whois

Here’s a tip for internet domain owners:

Make sure the contact information for your domain has more than one email address.  And make sure at least one of those email addresses is not in the domain itself.

If your email starts malfunctioning, you want people to be able to tell you about the problem … and if the only email addresses you list are in the actual domain, they won’t be able to contact you.

For example … if the mail server for example.com is having problem … and all the domain registration in the whois database shows ‘joe@example.com’, Joe won’t be able to be notified there is a problem.

The contact information is publicly accessible via the ‘whois’ databases.

Domain registrars that offer whois privacy capabilities should let you list more than one email address when they redirect the email address that they list in the whois look-ups.

For privacy sake, I like using a PO Box for the mailing address on all my domains.

Blocking Mailbait

Recently I’ve been getting a lot of mail from the feedback loops I subscribe to indicating that someone has gotten a subscription confirmation message and they considered it spam.

After digging into my logs I noticed a few things …

  • The subscription requests are being initiated from TOR exit nodes.
  • The web requests that initiate the subscription have “mailbait.info” as their referrer.

This ‘mailbait.info’ service is supposed to allow you to fill your mailbox … why anyone would want to do this is beyond me … and it has absolutely ZERO protections against submitting someone else’s email address.  As such, it just ends up generating spam.  And a lot of the twits that are using this ‘service’ are hiding behind TOR nodes, which protects their IP address.

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Android and sendmail

And you probably read in my last post … I had a problem getting mail setup my new Android phone.

I could receive mail fine … but it failed (with a totally useless message) whenever I tried to send mail.  I was sure I had the settings right (userid, password, ssl, etc).

I have my mail server configured to do authenticated sending (as all good mail server admin’s should) … but for some reason the authentication wasn’t working correctly.

I tried various setting combinations to see what might be the problem … I verified the settings with my iPhone and Thunderbird.  Everything matched up.

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DNS: Sends No Mail

I really wish there was a way to indicate, in DNS, that a domain never sends mail.

That way, if a mail server recieves mail claiming to be from that domain, it can be discarded out of hand.

I’ve got a bunch of domains that JUST do web serving … they never send mail.  If the web server that they are hosted on does send mail, it’s sent from via the midrange.com mail server (and is identified as such).

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Confidential Information

I saw a very interesting mail reject message today on one of my mailing lists …

You are receiving this message because you have attempted to send an e-mail containing confidential information. Examples of confidential information include, but are not limited to social security numbers, birth dates, account numbers, policy numbers, medical history, financial history, personal phone numbers and user IDs. Another example of sending confidential information would be combining any two or more of the following: name, address, identification numbers (employee number, phone number), organizational affiliation (place of employment). This information may be contained in the body of the message or any attachments.

I looked at the body of the message it was rejecting (which was included in it’s entirety), and noticed that the message referenced dummy social security numbers (the message discusses SQL techniques).

Of course, based on the warning message, it would probably reject ANY numeric text that was included in a message at all.

I suspect that the company, who’s server rejected the message, does not have a problem with email volume … since the majority of email sent to them is probably rejected.

I really wonder about companies that have such incredibly draconian content rules.  How do they stay in business?

Report as SPAM

It’s nice that many of the major mail providers give you the ability to report a message you’ve received as spam … but some of them make it far TOO easy to report something as spam.

I’ve noticed that many of the big names put the “Report as spam” button way too close to the delete button.

Let’s take a look at some of the providers …

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