If you were looking to employ someone, you’d carefully check their reputation and their references.  Email providers are now becoming just as cautious about who they accept emails from, in an effort to prevent large volumes of unsolicited commercial email (spam) from moving through their servers.  They’re turning to ‘blacklist’ services, to see if you’ve developed a reputation for being a known source of spam.  This month we look at blacklisting and how it can put a halt to your legitimate business emails. 

There are numerous blacklisting services on the internet, which use various methods to build up a list of known spam sources.  One such method is a ‘honeypot’ - pretending to be an unsecure email system, which attracts spammers and spamming software.  The blacklisting server then adds the internet IP address of where the spam came from, to the blacklist.  Email providers check this blacklist before accepting email and if the sender’s server is on that list, their email may be rejected before the recipients even see it.  This is different to spam filtering which actually checks the contents of the email itself.

Unfortunately, your own business can become blacklisted if one of your computers picks up a spamming software ‘bot’ or malware.  Like a virus, this malicious software installs itself onto your machine and starts sending out spam emails through your internet connection, however it may not be detected by your anti-virus software.  You can very quickly become identified as a spam source and blacklisted, which will prevent legitimate emails from being sent from your own local email server. 

The first indications of blacklisting are usually email failure error messages when you try and send a message.  They commonly refer to rejecting your email for ‘policy reasons’ and may or may not mention spam or blacklisting.  Email addresses that you’ve previously communicated with successfully may now start to reject your messages.

To tackle this, the first step is to confirm which blacklisting services you appear in.  Some services even provide a link in the email failure message with further information on why you were blacklisted, when it happened or the possible cause.  The infected computer then needs to be identified, removed from your network and thoroughly cleaned.  Your email server should also have its configuration checked to ensure it’s not an ‘open’ relay, allowing emails to pass through it which did not come from you and are not destined for you.  Once you’re sure your network is completely clean, you can ask to be ‘delisted’ from the services you’ve been appearing in.  Some services will action your delisting request as soon as they receive it, whereas some will take days or weeks and some services even request a payment to speed up the process for you.  The key to successful delisting is to make sure your computers are completely clean first.  If you make multiple requests to be delisted and you’re still generating spam, the services will start to ignore your requests and you’ll remain on the blacklists.