ISPs and Blocking Emails

When you send an email, your recipient's ISP (Internet Service Provider) ultimately determines if the email is sent to the inbox, or diverted elsewhere. Each ISP has its own rules for this -- some are lenient, and others are more strict, but in general, if the email is only a little suspicious, it may be delivered to the spam folder. If it's very suspicious, it may be bounced/blocked, and never delivered at all. This is a very important challenge in the digital marketing community, as deliverability is key. Let's take a look at what goes on behind the scene, and what you can do to get your email delivered to the inbox!


What is an ISP?

First, it's important to note that in a digital marketing context, an ISP is the company that provides the email address for your recipient (not necessarily their actual internet). This can include companies like AOL, Gmail, Yahoo, etc, that provide their users with an email account. This is important because, when it comes to email deliverability, the main factor is the recipient's email server, and the company that operates it. Every ISP scans all incoming emails for their user, and actively filters out any they deem to be harmful. Unfortunately, this can divert your legitimate emails as well.


What do they look for?

So, what do most ISPs scan for, specifically? ISPs scan incoming emails with the intention of protecting their user from dangerous content, including viruses and links associated with harmful software. The main thing to remember is this: although each ISP is different, in general they can only scan text-based content in your email, not images. This is important, because if your email is primarily composed of images, the ISP will register it as an email with most of its content 'hidden', and block the email. When sending your email, keep this in mind, and try to make most of the content in your piece 'scannable'.

ISPs also scan your email for certain words and phrases commonly associated with spam, so you'll want to avoid using any language that could be interpreted as 'spammy' ("special offer", "click here", etc). They will also flag any email containing too many capital letters, or special characters ("***", "$$", "~~<>**<>~~", etc).



In addition to scanning the content of the email, they also scan the sending email server against certain "Blacklists" (third party lists of suspected spammers). If emails sent from an account or website are marked as spam often enough, they will be placed on various blacklists, and all emails sent from that email server will be blocked. Any digital marketing platform must take all needed steps to prevent being added to them. While it is very rare, our email servers can make it onto a blacklist -- and we quickly take action to correct this.


Putting it all together

Keep in mind that each ISP uses its own criteria for marking emails as spam, and most use a combination of factors. You may not be able to always anticipate what a particular email server will mark as spam, but by following certain best practices, you can minimize the risk of your emails being diverted. For a more comprehensive list of these practices, please see:

How can I best avoid my email going to SPAM

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