Category Archives: Internet

LetsEncrypt certbot and Lightsail

Although not directly supported, it’s quite possible to use the LetsEncrypt certbot client on Amazon Lightsail Linux.

First of all … what is LetsEncrypt?

Let’s Encrypt is a free service that offers basic SSL certificates any web site.  The certificates are good for 90 days but can be renewed indefinitely. With the proper software, the installation & renewal of the certificates can be fully automated.

There are a few things to be aware of and workarounds that need to be done.

First, download the certbot-auto client itself…

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mailbait redux

For anyone who runs a mailing list and has gotten pummeled recently with a rash of subscription attempts, they may be coming from mailbait.info.

A while ago I blogged on how to block mailbait, but it appears they have changed their host.

Their new host is ‘themailbait.bitbucket.org’.

I suggest you update your web server configuration to block any referrer that references the word ‘mailbait’ in the URL.

Here’s my new httpd.conf entry to block mailbait…

SetEnvIf Referer mailbait mailbait
Deny from env=mailbait

Adding Envelope Sender in sendmail

Fair warning: This post is pretty darn technical and is of little interest to people who don’t muck around with Linux and/or mail servers.

Recently I had a problem with someone on a midrange.com mailing list where they sent obvious spam.

The problem was, they were a subscriber to the list and had posted before … so the normal counter measures for that didn’t work (the first post for all subscribers are held until approved, to prevent people from subscribing, posting spam, and unsubscribing).

The puzzling thing about this was … the ‘from address’ on the message was not in the subscriber list.

Turns out that Mailman will accept message based on the FROM address of the message or the SENDER address (also known as the envelope-from).  The sender addressed is set by the sending mail server and is not normally in the body of the message.

After a bit of digging around, I figured out a way to add this information to the message headers so I can more easily diagnose the problem in the future.

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Snow Days

As you might have noticed (or heard), the Chicago area has had a bit of snow recently.

Lots of people are off work because the the streets are impassible.

Ginny’s home, there’s just no way she could have gotten to her office.

Due to this contraption they call “The Internet”, and an invention called “VPN“, I have no excuse to not work.

In fact, I’m pretty sure there isn’t anyone in our office right now.

Thunderbird message list out of sync

Sometimes I find that the message list in Thunderbird gets out of sync with the message bodies. When this happens, if I click on a message in the list, the message body that is brought up doesn’t match the subject.

I found a easy solution … just shut down Thunderbird, delete the corresponding .msf file from the accounts data directory, and start Thunderbird back up. Thunderbird will rebuild the .msf file and everything should be fine again.

To find accounts data directory, click on the “Server Settings” category of the effected account and look at the “Local directory” field.

[tags]thunderbird, mozilla, email[/tags]

Net Neutrality

Ok, I don’t watch the Daily Show all that much … but I usually get a good laugh when I do catch it.

I found this clip, however, on the internet that’s pretty darn funny … it corrects some of Ted Steven’s … um … ‘errors’ that he made when describing what the internet is.

Say NO to Backup MX’s

Word of advice … with a few exceptions, there is absolutely no need for most organizations to implement backup MX’s. In fact, if they are not setup and managed very carefully, they can cause significant harm to an organization.

In the past week I’ve had two people on my mailing lists get their subscriptions suspended because their companies backup MX’s were not configured properly.

For those who don’t know, a “Backup MX” is a mail server that can accept mail delivery if the primary mail server is not available. A domain’s DNS records have “MX” records that list the mail servers in order of priority. Sending mail servers will try to connect to the first receiving mail server on the MX list, if that connection fails, it will try the next, etc.

Why are they not needed and, more importantly, why can they cause harm?

  1. Not needed
    1. Most sending mail server will try to deliver mail for a few days (generally around 5). Even if your mail server is down for a whole weekend, the sending server will continue delivery attempts.
    2. Unless your organization is expecting a massive amount of email (and I’m talking about thousands of mail deliveries per second, the kind a major national ISP might get), most mail servers are more than capable of handling the load … and the extra work involved in maintaining the additional servers probably isn’t worth it.
  2. Why harmful
    1. If not configured properly, mail delivered to the backup MX might not be accepted … thus causing non-delivery errors. This is what happened to the subscribers to my lists. Their primary MX was accepting mail, but the backup MX wasn’t. The rejection messages were being processed by the list software and their subscriptions were suspended
    2. Backup MX’s are often not as spam & virus resistant as primary MX’s. For this reason, spammers and virus writers often target backup MX’s instead of primary MX’s.

In the end … backup MX’s do have their uses … but only if implemented where absolutely needed and managed very carefully.

Oh, and by the way, if you are having problems sending mail from a different system than your primary mail server … it’s not because you need a backup MX. It’s probably because the other system needs to have a reverse IP name setup in DNS. Many mail servers are configured to reject mail sent from systems that do not have reverse IP dns entries setup.

[tags]SMTP, mail, email, Mail Servers, MX records, DNS[/tags]

Google Secrets Out

Google have recently filed a US patent which reveals a great deal of how they rank your web site. Some of it you could never of guessed at…

Great Site Ranking in Google The Secrets Out

This is a very interesting read.

I am not, as a rule, all that concerned with search engine rankings for my sites. The number of sites that cover the same topics as I do are pretty small. Thus, if someone is looking for information, chances are they will stumble across my sites.