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Why is my Email Marked as Spam?

Why is my email marked as spam?

There are so many possibilities, it’s difficult to know where to begin.

I will tell you that there is no simple solution to guaranteeing your email is never flagged as spam. Why? Because if there were an easy solution, spammers would use it, rendering all spam filters ineffective.

Let’s look at some of the factors that may contribute to your email being flagged as spam.


A word I’m going to use repeatedly here is “reputation”.

Spam-filtering technology has advanced in many different ways. Rather than focusing solely on the contents of each specific email message, filters now keep track of and factor in the past behavior of an email account.

Reputation is primarily based on people identifying spam and marking it as such when they see it. This data is collected and analysed in several different ways.

And naturally, a bad reputation can result in email marked as spam.

Your reputation

Spam CanYour email address – the “you@somerandomservice.com” part of your email message – may have a reputation, and that reputation may be good or bad.

As I said, it’s based in part on how many emails have been sent from that email address that have been identified as spam. If there’ve been a lot, then your reputation is poor, and more of your email will be automatically flagged as spam in the future.

Given that spammers regularly “spoof” the From: line of the emails that they send, it might not even be your doing. Hopefully, most spam filters account for this and don’t factor those messages in when they can identify them, or don’t factor in email-address-based reputation at all. Unfortunately, as we’ll see later, all spam filters are not created equal.

If others have ever blocked you, for example, then this data may feed into your email address’s reputation.

Your reputation with a specific recipient

Many spam filters analyze spam at both a global level – identifying messages that would be considered spam by anyone – and at the individual level.

If you have one individual that regularly marks your email as spam, for example, then your messages to that individual are more likely to be automatically marked as spam in the future. This may, or may not, impact your messages to others, depending on how the spam filter factors it all in.

The net result is that email you send to one person may be much more likely to be marked as spam than the exact same message sent to someone else, simply because your reputation with the first person is poorer.

Your email provider’s reputation

Your email provider carries a reputation as well.

Email providers that are known to be regular sources of spam, or are known to have lax security (allowing accounts to be easily hijacked) may have a poor or negative reputation. That means that email sent from any email address using that provider stands a slightly higher chance of being flagged as spam.

It’s a form of guilt by association.

The most obvious examples are free email accounts, which by their nature let anyone create an account, including spammers. Hotmail, specifically, was a source of much spam for many, many years, and its reputation still suffers today.

Your email server’s reputation

This is a little more obscure, and to understand it we need to review the path that email takes on it way to your recipient.

The message is sent by your computer to your email provider. (Skip this step when using web mail.)
The message is sent by your email provider to an email server, with instructions of where the message is to go.
Next it may be sent to one or more intermediary servers, each with instructions to forward the message on to its intended destination.
The last server in that chain (potentially just your email provider’s server, if no intermediaries were needed) delivers the email to your recipient’s email server.
The last server in that chain – the server that finally delivers the mail to your recipient’s email provider – has a reputation as well. Typically identified by IP address, that server may even be on black lists, the ultimate in poor reputation.

What this means is that the ability of a message to make it through also depends on the path it happens to take on its way from your email service to that of the recipient.

The reputation of the content of your email

Naturally, the content of your email is not ignored. The words and phrases you use are part of the complex spam detection equation – but perhaps not in the way that you might think.

Without a doubt, certain words qualify. Anything from some types of medications to body enhancement options to promised cash from a Nigerian prince are almost certainly used to identify spam.

But spam filters are also looking for anything common across email messages that many people mark as spam. For example, if the phrase “make money fast” is present in many messages that a lot of people mark as spam, it garners a bad reputation. Its presence in your message may be a strike against you.

By itself, using a word or phrase that many people also see in emails they mark as spam is probably not enough to doom your message to the spam bucket. In conjunction with other things, however, it could contribute to it.

Spam for one is not spam for all

All those rules, and many more, I’m sure, factor in to whether or not your email will be marked as spam.

But it gets worse.

Different recipients use different spam filters. Different spam filters use different rules, have different ways of factoring in those rules, and have a different set of “reputation” filters built over time for the various aspects of spam on which they track reputation.

And some don’t track reputation at all, relying on only the most rudimentary tests, like black lists and offending word or phrase lists.

Spam filtering is an incredibly complex process with incredibly complex – and vague – rules.

Part of that is on purpose. As I said, we don’t want there to be a simple answer to the question, “how do I avoid having my mail marked as spam?” If there were, the spammers would start following those rules immediately.

Best practices

The “right” solution is to follow best practices, which can be summed up in two statements:

Avoid guilt by association: use legitimate and reputable email services.
Keep your own reputation clean: don’t send emails that your recipients might mark as spam.
The nuclear option

In my opinion, if your reputation is clean and your email is consistently being placed in your recipient’s spam folder, the options are actually fairly limited.

I’d start by using a new email provider, and potentially even a new email address. Chances are there’s something about your existing situation that the recipient’s server just doesn’t like. Given that their IT people can’t figure it out, and it’s apparently out of anyone’s control, taking steps to avoid the problem – typically, avoiding that guilt by association – is about the only thing I can think of to do.

Originally Posted on the Ask Leo web site