Every Arrow Technology email server has four anti-spam systems.
The first system blocks email spam mostly by using block lists, which are commonly used lists which are mantained by various organisations. Many spammers will get detected when they spam fron specific computers and get added to these block lists.
Bear in mind that spammers often infect other peoples computers, so sometimes legitimate email servers might be blocked if they are sending spam. If a computer is a prolific spammer, they will stay on the block list for a very long time or permanently, but many computers subsequently stop sending spam and might be removed from block lists in as little as just a few hours.
This first system will also block some 'legitimate' email servers that have been incorrectly configured. Unfortunately, these badly configured email servers look exactly like spammers. Some are unwittingly even used by larger organisations, where their IT and service providers are either unaware or don't care. Probably the organisations would care, but they don't know.
We do not see huge numbers of these bad servers compared with the number of correctly configured email servers, but they do appear every so often. This is absolutely a problem with the sending email server and those servers should be fixed; the causes and fixes are welll documented and easy to demonstrate. We have an auto-whitelisting feature that significantly alleviates the problem and yet still allows us to block lots of spammers.
Anyone that sends an email that is blocked by this first anti-spam system should very quickly (normally instantly) receive a bounce/non-delivery notification from their own email server, because the checking is done before the email is accepted for delivery and therefore their sending email server can be given the notification.
The second email anti-spam system is based more on the content of the message, is a more involved analysis and tends to be very accurate; it very rarely blocks legitimate emails. It also supports a good level of customisation of the checking process.
Arrow Technology actively maintains a centralised list our own rules which are then automatically distributed to all of our email servers. Spams vary over time and there are often specific messages that appear regularly at any one time. We analyse common spam messages and use our rules to assist with blocking them.
Anyone that sends an email that is blocked the second anti-spam system may not receive a non-delivery notification, because the checking is done after the email has been accepted for delivery. That means the sending email server has already gone before the reason for rejecting the email is known, so the sending server cannot be told about it.
Unfortunately with spam rates being so high and many spams attempting to look like legitimate emails, it is impossible to stop all of them. If you are using our email services you will probably receive some spam messages, but hopefully not many.
Bear in mind that you can call or email us to discuss any specific email issues. Email services are very important and we will assist with discovering any issues with emails that you either send or receive (or did not receive).
For websites, our SiteSentinel has spam account registration blocking where new account registrations are analysed and will be blocked if they match a variety of checks.
SiteSentinel also has sophisticated form spam blocking which uses a score based analysis system, similar to email anti-spam, to block things like contact form spams.
If you get similar or repeated spam through your website, please let us know and there is a very good chance we can block it.