Blacklists - why did we block an incoming email?

If you are not receiving email from someone and your email is hosted or forwarded by us, it may be due to spam filtering.  

This blog explains what spam filtering systems we have.

Black list filtering

We subscribe to a number of quality "black lists". eg SpamCop, SpamHaus, Abusix, and more.   These services identify IP addresses that are sending high volumes of spam (as determined by people who mark an email as spam. It's a complicated system, where each black list gets their data from different service providers. So each blacklist has a different perspective on who is currently a bad sender. If anyone of them mark a server as bad, then the server is bad, and we won't accept email from that server.  

Any ISP, and including reputable professional email services like Microsoft and Google also get black listed (or get some servers blacklisted). It is a manual process that requires the ISP to communicate with the blacklist, and identify whats steps they have taken to mitigate the issue to be come "delisted".

Many services would like to be "white listed", but that it is not common. The issue is, that it only takes 1 compromised email account to be hacked, and to send hundreds of thousands of spam emails. What black lists do is they block that specific server to stem the attack, but unfortunately, all the reputable email senders on the same server are affected with non delivered email. 

Often our customers come to us and say that they cannot receive emails from their customers. This is because their customers mail servers have been blacklisted by a blacklist we use. We need to use these black lists to stop spam getting through.  

If a few customers tell us of an issue, we will understand there is an issue, but we cannot do anything about it. If dozens of customers tell us of an issue, and it lasts for days, then we will consider turning off a blacklist. We do not take the decision lightly, as in doing so, the amount of spam that will be recieved by our customers will be alot. The subtlely here, is that it is best that the sender of an email, raises the issue with their mail provider, and not you. They should resolve their email delivery issues. We cannot resolve the issues for them. However, if a blacklist goes rogue, we also need to consider that. But we cannot fine tune the solution. It's a big switch, on or off. 

Spam Filtering

In addition to the blacklists, we run spam filtering software that looks at the content of emails, and makes a decision on how spammy it looks. We use an industry standard service called spamassassin that will give a score to every email recieved. We block the really obvious email. It remains possible that a smart IT person might also be able to block grey emails, with a lower score, if they like. We want to avoid false positives ourself. 

When are emails filtered?

Any time an email is received my our mailserver, ie. an email for any domain name that we provide email services for, then it will be checked by our spam filters. So all incoming email is checked for spam, even if it is a fowarded email.

We do not block outgoing emails (including bulk email), that is we do not block emails going from your computer to a destination email address, as our server is not involved, irrespective of your from address. 

Out Bound Email Policies

To ensure the good reputation of our email servers, we have an enforced limit of 200 emails per day. Most ordinary people to not send more than 200 emails a day. Most people who need to send more emails will use a bulk email service, or some other cloud service like CRM or accounting systems that send monthly statements. Should you be using "old school desktop software" then you may need to request an increase of your sending limits. We can do that for people on higher hosting plans, however, you must agree that you will install anti virus software, and that you will pay for systems administrators time to resolve and restore our good email reputation in the case where your servers were compromised causing our servers to be blacklisted (that would negatively affect all our other customers) 

Where do blocked emails go?

We delete blocked emails. We do not provide spam folders sorry. We almost never get a "false positive". If a customer is ever blocked by our spam filter, they should get a failed delivery report, but this is subject to their own preferences settings. We either deliver an email, or return a failed delivery code. There is no black hole.

Why else might an email not get delivered?

• Attachments bigger than 20MB
• It contains a virus
• Their mailbox is full
• Incorrectly typed email address, either sender or receivers.
• The senders email domain name is expired or non existant, or experiencing DNS issues.
• The sender SPF, DKIM or DMARC rules indicate that the sending IP is not permitted to send this email, or is not signed with a valid signature.