Why You Should Rethink Email Attachments in Your Marketing 

email attachments in marketing cover image with a trash paper

Email marketing tools usually won’t let you attach files because attachments can trigger spam filters and significantly damage deliverability. 

Sending an attachment to one person is pretty straightforward; every email client lets you do it. You might think using attachments is also a great way to share content like PDFs, video clips, and podcasts with your subscribers. 

But you’ll quickly find out that mass email platforms don’t allow email attachments in marketing. And there’s a good reason for this.

Let’s explore why this restriction exists and how it impacts your strategy.

How Spam Filters Treat Emails With Attachments

Spam filters are essentially machine learning algorithms designed to keep unwanted emails out of your inbox. Let’s explore how they work in simple terms. 

The Bayesian spam filter is the simplest type of spam filter. It uses basic probability principles to determine whether an email is spam. 

Once an email arrives, the filter looks at everything, from the email content to the email headers and the attachments. It compares the features with its database of previous spam emails to calculate the likelihood of a new email being spam.  

Bayesian filters are pretty cautious about attachments, especially with mass emails. When you send an attachment to a single person, the potential security threat is limited, but with bulk email, the threat could multiply and grow out of control. 

Spam filters consider: 

  • File extension: Executable files (.exe) or script files (.js) are more suspicious because they can run harmful programs on your computer.
  • File format: Each file type has a unique signature. So, even if someone intentionally changes the extension to hide the file type, the filter can analyze the file structure to identify the actual type. 
  • File content: Sometimes attackers hide a script or file inside a larger file. Spam filters analyze file contents for these irregularities. 
  • File size: Huge files can overload the system or hide large amounts of unwanted data. On the other hand, tiny files might contain scripts that download more malicious software once opened.

Some filters also analyze how the attachment is presented in the email. An email that tries to push you to open an attachment immediately or uses urgent language looks suspicious. This is because, when performing phishing email attacks, spammers often create a sense of urgency to trick people into opening attachments without thinking.

Other Reasons to Restrict Attachments in Marketing Emails 

Apart from security concerns, there are additional reasons to steer clear of using attachments in marketing emails.

Attachments Are Hard to Track 

Email marketing tools and email tracking software allow you to track open rates and other important campaign metrics

This feature isn’t available for attachments. Unless you have another way to gauge the attachment’s open rate — like asking the readers to do something after opening the file — there’s no way to see how many people downloaded and opened the attachment. 

Attachments Take Up Server Space

Email attachments can eat up a lot of server space, especially if you send them in bulk or if they’re large files.

Processing large amounts of data is time-consuming, meaning messages will take longer to send. Slow emails are frustrating for both senders and recipients. So, mass email services eliminate the problem by restricting attachments. 

What Are the Consequences of Email Attachments in Marketing? 

So far we’ve talked about why attachments are restricted. But even if you come up with a way to send email attachments in bulk email, it’s still a bad idea. 

Attachments in marketing emails can lead to: 

  • Reduced deliverability. Mass emails with attachments almost always end up in the spam folder. This means you’ll have a lower inbox reach
  • Lower sender reputation. When your emails frequently end up in the spam folder, it will send a red signal to the ISP to flag you as a spam sender. This can hurt your sender reputation, and more of your emails will find their way into the spam folder. 
  • Tarnished brand reputation. If your emails keep going to the spam folder, your customers and users might start seeing you as a spammer, especially if you don’t have a strong relationship with them. This can create a negative image of your brand and damage your business’s reputation.
  • Wasted resources. You invest time and money crafting your email campaigns, but if they end up in spam, you won’t see any return on investment with your email marketing. This means all your effort and spending are wasted since your emails aren’t reaching your audience.

Alternative Ways to Share Files with Subscribers

So, if email attachments in email marketing are frowned upon, what are you supposed to do if you need to send a file to your customers? 

How can you deliver the lead magnets your promise to encourage them to subscribe? 

Include a Link To the File 

The best way to send files to your subscribers and avoid triggering spam filters is to host the file outside the email. For example, you could upload the file on your own website. Then, create a public link to that file and include it in your email.

Another excellent option is using cloud storage. Services like OneDrive, Google Drive, Apple iCloud, and Amazon Web Services let you share files widely and easily. And they have a positive reputation with spam filters. 

Host the file on one of these platforms and share the link through a strong call-to-action button in your email.

This method has three advantages:

  1. It’s straightforward. Just pick a hosting platform, upload your file, and generate the link.
  2. It’s usually free. Many services offer free options, depending on your needs.
  3. It’s trackable. Unlike attachments sent directly in emails, you can see how many subscribers have downloaded your files.

Embed Images

If you decide to share images or videos with your subscribers in your email copy, you can embed them using your email marketing software. Most tools offer drag-and-drop or HTML code to include the image inside the text. 

However, this approach can cause problems if you overdo it: 

  1. Visibility issues. Email clients allow users to block images. So, you may not be able to show your images to some subscribers. 
  2. Spam concerns. Spammers try to bypass spam filters by hiding certain words and phrases inside images. Because of this, ISPs might block images that contain text. 
  3. Responsiveness. A lot of people check their emails on mobile devices. If your layout isn’t responsive, your images might not display properly on smartphones and tablets. 

Remember to keep the number of images limited to one or two. Jamming your email with images is a bad email marketing practice that can trigger spam filters. 

Ask Subscribers to Reply to Your Email 

This method works best if you have a small number of recipients. Instead of sending the attachment to everyone, you can email them first to ask if they’d like to receive it. Those interested can reply to request the attachment. 

If you go this route, ensure the file format is universally accessible and avoid large files that are slow to download and clog up email storage.

Also, be careful with the file name. Avoid misleading or spammy names. Keep it short and clear so it’s easy for recipients to save and recognize on their devices.

Can I Send Attachments in Cold Emails? 

At Campaign Refinery, we have a tough stance against sending cold emails and immediately terminate the accounts of users who engage in this practice. 

But let’s assume you need to reach out to a few people to present your products or services. Is it okay if you attach your brochure or product details?

The answer is still no. 

Your goal with your first email is to establish trust. Even if your emails steer clear of the spam folder, your recipients don’t trust you. Sending an attachment when there’s no established trust can make your email seem even more suspicious. 


  • Keep it brief: Respect the recipient’s time by keeping your email brief and to the point. 
  • Focus on the message: Write a clear, concise email that introduces who you are and what your company does. 
  • Offer value: Explain the value you offer without sounding too salesy. Share insights, offer a small piece of free advice, or discuss a common challenge in their industry. 
  • Invite to a conversation: Invite the recipient to discuss their needs and how you might help. 

Ditch Attachments And Thrive in Email Marketing

At Campaign Refinery, we focus on making sure your emails reach your audience every time. 

We know how tricky it can be to manage email deliverability, and we help you connect with your audience in the most effective way possible. 

We believe that following sound email marketing principles means you won’t even need to think about using attachments.

Why complicate things with attachments that could send your emails into spam oblivion?

We equip you with the tools to grow your subscriber list and engage your audience using safer, more effective methods. Think of us as your toolkit for clean, high-deliverability email marketing. 

Apply to join Campaign Refinery today and start sending smarter marketing emails. 

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