Email Archives

How to remove an IP from the CBL (Composite Blocking List)

Today I was introduced to something called the CBL, or the Composite Blocking List. This is one of several Spamhaus projects that’s there to make sure IP’s are blacklisted when they’re sending spam.

You can check if your IP’s are OK at http://www.spamhaus.org/lookup/

The CBL is a separate website in which you can also lookup IPs. Spamhaus will tell you if that’s the case and direct you to the CBL here: http://www.abuseat.org/lookup.cgi

Even though my IP was otherwise fine, it was listed in the CBL, and Yahoo kindly made me aware of this as part of an error message I’ve received when trying to send an email. If ever there is an email problem in CentOS, the first place to look is /var/log/maillog. Here’s Yahoo’s very helpful explanation: https://help.yahoo.com/kb/postmaster/SLN5070.html

Turns out that the hostname was not setup yet, so the box would respond as localhost.localdomain. That’s a big fat no-no as far as the CBL people are concerned. Here’s CBL’s explanation:

This IP address is HELO’ing as “localhost.localdomain” which violates the relevant standards (specifically: RFC5321).

The CBL does not list for RFC violations per-se. This _particular_ behaviour, however, correlates strongly to spambot infections. In other words, out of thousands upon thousands of IP addresses HELO’ing this way, all but a handful are infected and spewing junk. Even if it isn’t an infection, it’s a misconfiguration that should be fixed, because many spam filtering mechanisms operate with the same rules, and it’s best to fix it regardless of whether the CBL notices it or not.

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How to open SMTP port 587 to send emails in Plesk

By default Plesk on Linux uses Postfix for outgoing email, and by default listens on port 25 for outgoing SMTP mail. Some service providers do not allow to send emails on that port, and tragedy occurs: clients can’t send email with their Plesk servers. Not good. Other SMTP ports will usually work, such as the … Read more

How to setup Plesk Mail in Mozilla Thunderbird for Windows

In this episode I’ll show you how to setup Plesk Mail in Thunderbird for Windows. Unlike most email clients, Thunderbird can figure out the correct settings by itself – something neither Outlook nor Mac Mail can do. Therefore, the real magic with Thunderbird is figuring out how to get to the account settings. To do … Read more

How to setup Plesk Mail in Microsoft Outlook for Windows

In this episode I’ll show you how to setup Plesk Mail in Microsoft Outlook on Windows. It’s often a big stumbling block for users. The instructions will also work for Microsoft Essentials, the predecessor of Outlook Express. I’m using Outlook 2010 here, but the instructions are also applicable to later versions. The two important windows … Read more

FIXED: WordPress refuses to send you a Password Reset Link

I ran into an interesting problem today: on a CentOS 6 server a colleague of mine wanted to reset her WordPress password via the handy link provided in the login dialogue. But rather than sending an email, WordPress got back to her with the following error message: The e-mail could not be sent. Possible reason: … Read more

How to install and secure Dovecot in Plesk 12

I’ve just installed the Dovecot Mail Service on one of my Plesk 12 servers. It’s an alternative to the old favourite Courier IMAP/POP and a new addition in Plesk 12. Dovecot does more or less the same as Courier (i.e. lets you receive mail), but it’s a bit more configurable and debug friendly. It also offers … Read more

How to override auto-detected Email Settings in iOS

The nature of any automation is that sometimes it just doesn’t work. Apple’s iOS is no exception. When you add a new email account on your iOS device, several mail providers’ settings can be auto detected. It’s there to make our lives easier so that we don’t have to add details for mail servers and ports … Read more