Deliverability just means the ability of your emails to enter the mailboxes of your targets. You might not think about this, but cold outbound is a game where losing can come with a high price. If your messages get flagged as spam, or the emails you send to aren’t:

Uniqueness

Back to spam filters. No one knows exactly how they work. If we did, every email marketing agency would immediately change their copy to beat the filters, which would defeat the point. However, one pretty clear thing that makes a difference is the uniqueness of the message you're sending. If you send 1,000 emails, all with the same copy, they'll likely be flagged as spam. There are several ways to increase the uniqueness of your messages.

A popular (but controversial) one is Spintax, which generates multiple variations of a piece of text and randomly assigns them to each email. Some people say this doesn't matter at all, some say it matters a bit, and some say it's the only way to beat the spam filters. {It usually looks like this.|It can look like this.|This is how it sometimes appears.} If you generate three emails using that copy, you should get three unique versions of your email. 

If you add two more {like this|such as this}, it'll potentially generate six unique versions. You can keep multiplying these different spintaxes to get a rough measure of how many possible versions might be included in your message. Make sure that you do not only add the same number of spintax variants (for example, three versions for one and three versions for another) because it'll stop the randomization part and generate only three versions. 

Another necessity in 2025 is to have AI generate portions of your email and then pass these AI-generated bits of text into your email as variables. This could be things like the ICP of the business or a complex PS line based on some scraped data about the person. AI is not yet good enough to generate a complete email without any human input (although this is certainly on the horizon) – but these small chunks of text passed into the text of your email are a great way to make sure that you have a lot of uniqueness in the email. If possible, aim for at least 45% of your email to be AI-generated.

Spam Filters 

As I mentioned before, spam dodging has become the default for almost every email client. Often, it is the big selling point they use to get people to use their products. Understanding how to beat spam filters is tough because the rules change all the time, and the ML models they use are constantly improving. Here are some of the basic rules to follow, although this is by no means everything:  

Links are a one-way ticket to the spam folder. Even unsubscribe links. If you absolutely must add one in your signature, do Example(dot)com, the (dot) thing does work if you need to send them somewhere. If you have something of extreme value like a personalised video using Sendspark then send them from email 2 only but test this carefully as your email infrastructure will degrade faster. Is the increased response rate worth it?

Images tank your deliverability. Full stop. Learn to paint pictures with words. It's called writing. Master it. Some websites will tell you that adding alt text or linking to an external image will help with deliverability, but the reality is that an email with any images at all is probably not worth the risk to your infra. 

Think about it as though you were the Google Spam AI. Ask yourself two questions about your copy:

1. Does it sound like the sender knows the receiver? 

2. Does it sound like they are trying to sell something?

If you answer no to 1 and yes to 2, you are probably going to get filtered. Again, if you act like spam, you'll get treated like spam. That's why you have to do your research and learn enough about your client to tell the spam filters you really sent the message yourself. 

Bad Analytics

FYI: do not track your open rates. The way open tracking used to work is through a "tracking pixel," which is a pixel embedded in the body of an email that, when loaded on the image hosting site, would tell you that it was opened. Recently, email services have gotten smart about this, sometimes blocking these pixels or automatically loading images when receiving email, skewing the open rate. You're much better off using the reply rate as your measure of success.