The are two factors that can conspire to frustrate an email marketer's efforts. One is the ease with which people can subscribe to an email newsletter, the other is the ease with which they can set their spam filter to block them.

There is an argument that says you should make it as easy as possible for people to sign-up: just collect their email addresses and do not trouble them for anything further. That could be a missed opportunity, but it could also create a problem later if they sign-up on a whim having seen something that was only of interest at that moment in time. I know, I do that all the time.

You can easily create channels or topics so subscribers can choose which of your messages they wish to read. If you do that and stick to them in future mailings - and there are systems that will help you - you will keep their interest. If you don't, you risk losing their interest over time until you send something you really want them to read only by then they are already filtering you out.

My argument, therefore, is that you should make it as easy as possible to unsubscribe: it is counter-productive not to do so. If you don't offer an obvious and easy way out, human nature means they will take the next easiest method which is to block all your messages using a spam filter.

There are several dangers from spam filters. One danger is they can junk all email from a specific domain, like ...@yourdomain.co.uk – so it's goodbye to everyone in your business. Or they can filter by key words within the mailshot, like your brand name. And they can filter-out according to the destination address. Some smart surfers use different email addresses whenever they subscribe to something – subscribing to you as theirname01@gmail.com and to something else as theirname02@gmail.com, say. That makes it very easy to filter your email out if they later choose to, they also do it so they know who has passed on their email address when they shouldn't have.

If, as you should be doing, you are tracking marketing data, that could be skewed as a result. Your numbers are going to include a lot of subscribers who you think are reading your messages but not responding. Over time, as you are added to more spam filters, that response rate will mysteriously go down, despite your best efforts to tweak and tune your messages.

An email marketing campaign should be an iterative process, and there are tools and services that can help you develop a successful strategy. As well as dealing with bounced emails from "dead" addresses that are automatically removed from the system, the more sophisticated ones can track subscribers who are not opening their emails from you. That sounds pretty clever, but it is quite possibly one of the most useless pieces of information you can gather. Important, but nonetheless useless in the sense that there is nothing you can do about it.

Once you are being filtered out, you can't even send them an email to ask why they aren't reading your emails. It is the ultimate rejection. Even worse, if they send you a message and forget they've already added you to their spam filter, they will never see the reply from you that they are expecting.

You shouldn't see this as a process of removing "dead wood" from your lists, you should see it for what it is: a potential customer who was at one time interested in your message but who now will never hear from you again.

In my books, being added to a spam filter must count as a minor marketing disaster. You must make it easy for someone to unsubscribe instead. That may seem paradoxical, but a cancelled subscription is far less harmful to you than being added to a spam filter. You part on good terms and it allows the possibility they may subscribe again at a later date. From my own point of view, if I keep seeing messages I am no longer interested in reading and it is not immediately obvious how to unsubscribe - and easy to do - then adding it to my spam filter is the quick and easy solution.