A Short Guide To Email Attachments: The Do’s And The Don’ts

email attachments

Email attachments are one of the certain ways to attract your recipient’s attention.

What are email attachments? They are files that are added to the email message bringing extra value to it. These may be files of different formats, sizes, and contents.

Adding an attachment is pretty straightforward, but there are limitations, especially when it comes to email campaigns. Which is why we’ve created this short guide to explain the do’s and don’ts of attachments in emails.


The element of trust: email attachments may seem suspicious

Attachments are often used by marketers when writing a professional email as a way to give more value to the message and incentivize the user to open an email. If you are trying to reach out to a specific prospect and use attachments as a sort of personalization method, it might work.

But when we are dealing with cold emailing, including anything else besides the actual text content can seem shady.  This may sound obvious, but many marketers forget that when the recipient receives a message with an attachment from an unfamiliar source, they are likely to believe it’s malware.

Cold email isn’t a bad thing per se, but attaching a file to it makes it look far more suspicious and makes it more complicated for emails to avoid spam filters. This can put your email in the spam folder or worse, labeled by the ISP or mail client, inevitably hurting your sender’s reputation and harming your future email campaigns.

Moreover, many people ask “Should you explain attachments in business emails?” The answer is a resounding “yes”, of course. Explaining the attachment makes it a bit more trustworthy. This is why you should try not to send an email message that contains an attachment only – it doesn’t look professional at all and doesn’t raise any trust.

IP or domain reputation: attachments have a negative impact 

Once again, using attachments in cold emails can throw a wrench in your campaign. Bulk cold emailing using attachments is likely to result in a high number of complaints. Every domain on the web is identified by ISP before it’s processed, allowing to block pirate content or adult web pages through the labeling of domains and IPs. A high complaint rate can catch your ISP’s attention.

In our case, the IP or email address you use for cold emailing can be flagged by ISP, and your email messages will either end up in the spam folder or completely blocked.


Therefore, email attachments in cold emails can lead to the deletion of your email domain name from a list of reputable sources. Use them only in small personalized email campaigns or with your existing clients.

Attachment formats: a wrong format can lead to an email block

So you’ve decided to use an attachment for your campaign email. You need to make sure people will feel confident and interested enough to open it. First of all, your email message in itself must convince the receiver to open/download the email attachment. If that’s not a problem, be mindful of this one rule.

Never send anything besides documents or images. In most cases, the user will never download anything besides a clearly visible document or image. It’s best to keep your attachments in .txt, .jpg, .gif, and.pdf formats.

PDFs make a great addition to any nurturing email, but they can be difficult to create and edit. You can find out how to edit a PDF easily from our friends at JotForm.

If you still need to send a file in a different format, make sure you are using an acceptable email attachment format because every ESP has its limits on file formats (for example, look through at Gmail attachment limits).

Size limits: follow email attachment limits for good deliverability

Want advice on the size of email attachments? Email servers and clients have email sending limits, so make sure you follow them. Moreover, email clients may reject your email as a whole because of its size. Try to keep your email message body within 15-100kb, with files no bigger than 10mb.

If you need to send a bigger file, it’s safer and generally more acceptable to attach a link to the file on Google Drive. Besides hosting large files, Drive will check the file for malware, solving the trust issue.

The email attachment size limits described above are considered universal if you don’t want to get caught in a spam filter.

Deliverability: attachments can keep your email from reaching the inbox

Reducing the attachment size of your email is one way to increase the deliverability of your message.

Having an attachment won’t automatically ruin your deliverability. Email clients won’t filter you out for having images between 20kb and 50kb in size. However, if you decide to insert a half a megabyte image, you are not safe from being labeled red by the email client.

This happens because email spammers love to use images to hide the text of their messages, undetectable to filters. To keep your deliverability high, stick to under 60kb image attachment size limit. This research by EmailOnAcid goes into more detail on the effect of the file size on deliverability.

HTML email attachments: files may not be displayed correctly

An attachment is not just a file: it can be an HTML styled template with text in it. Companies tend to use those for promotional content instead of plain-text emails.

With styled HTML email attachments, you can create content that’s far more appealing than plain text. The problem is these templates often don’t load well on every device and email client. In fact, not all templates are even optimized for mobile view.

And while using HTML templates can help you utilize colors in email marketing to improve conversions, they should be used carefully. Keep those two points in mind when choosing or creating a template.

Additional tips

How to add attachments to email? Here are the final tips for you to follow:

  • Use attachments as additional information to plain text emails. Take advantage of cold email formulas to easily convert leads.
  • If you use email templates, make sure they don’t overload your email size-wise. Check the email sending limits of your ESP to know your email size limit.
  • Unless the file you’re trying to send is highly personalized (a ticket, a personal invitation, a document, a custom report etc.), you have higher chances using a link to the file instead of the attachment.
  • Save email attachments for campaigns to existing customers and warm leads.


While email attachments are a usual sight for marketing emails, there are certain rules you have to follow to keep your email deliverability high. If you’ve already taken care of your sender reputation and always use an email checker to clean your lists before sending, the main characteristic you still have to pay attention to is the attachment size limit – the smaller the file, the higher your chances to get into the recipient’s inbox.

Try to avoid sending files to cold leads: your email can be deleted or reported if there’s no established relationship between you and the recipient.


  1. What would be a good way to send an attachment in an email campaign? Or should attachments in campaigns be avoided completely?

    1. Thank you for your question.

      Attachments can have a negative impact on the email deliverability, that’s not a secret. Though there are some tricks you can use. For example, if you need to send a video, you can try some alternatives out: cinemagraphs, a pic with a link, GIF, etc. You can read more about it in the guide written by our friend from Movavi here: https://snov.io/blog/video-in-email/

      Also, if you need to send small files that do not break the ESP’s sending limits, that’s Ok and you don’t have to worry. Just check the email delivery rate regularly.
      Good luck with your email campaigns!

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