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Is there a limit to the size of Email Attachments?

Is there a limit to the size of Email Attachments?

When sending emails, larger isn’t always better, especially when it comes to file sizes. Sending large images or sending large HTML files can negatively affect engagement and deliverability.

Does your email campaign need a kilobyte diet? Here are some best practices to make sure the size of both images and HTML code (email attachments) is just right for your email campaign.

What does email file size mean?

email file size

In terms of file size and deliverability, you might be surprised to learn how low the tipping point is. Large email files can seriously harm your chances of reaching the inbox – not good for an email marketer looking to break through.

However, what impacts the size of these emails? Well, when we talk about limiting file sizes in email, we are talking about either:

  • Various images- Make your email campaigns stand out with photos, logos, images, and branding.
  • Coding in HTML- You can include live text and building blocks in your email marketing campaigns.

Best practices for image size in email attachments

The results of a study by Email on Acid find that varying image sizes, from 16KB to 696KB, do not affect delivery. However, this doesn’t mean you can just throw big images at the audience.  

If your email is too large, it may take a long time to load and your subscribers may delete it before it has been downloaded. 20% of Americans receive over 50 emails a day – people won’t want to waste their time on emails that take too long to render.

When a mobile data plan is limited, large images will consume valuable megabytes. Think of a demographic that is primarily reliant on mobile technology for email access (students, low-income families, older demographics, subscribers in emerging markets). You will not be appreciated if you run those data-hungry, slow-loading campaigns.

Additionally, emails containing large images and little or no live text can be flagged as spam by spam filters. To circumvent spam filters, many unscrupulous senders use graphics to represent text that cannot be read by machines to disguise dubious content.

To optimize delivery, we recommend that you always maximize the ratio between text and images by aiming for at least a 60/40 ratio and keep your images under 200KB.

Optimum HTML file size for email designers in an email attachment

The size of HTML files does seem to affect email deliverability unlike the size of images. A series of HTML emails of varying sizes, ranging from 15KB to 650KB, was developed by our friends at Email on Acid to conduct the test.

Unsurprisingly, the smaller files landed in the inbox without any problems at all. Despite this, deliverability became a problem once the file size surpassed 100KB. This is because spam filters consider any unnecessary code in an email as possibly dangerous, potentially serving as a conduit for viruses and malware.

The emails failed multiple spam filters as soon as they reached 110KB. The list includes spam filters implemented by some big players in the email eco-system, including Apple Mail 5, 6, and 7, Google Apps, Outlook 2007 and 2010, and Yahoo Mail. There is no doubt that a considerable number of your subscribers will never see your emails if they do not reach these inboxes.

You can reduce the size of HTML email files that are larger than 100KB by following these steps:

  • It’s always better to remove unnecessary spaces, carriage returns, and comments in your HTML.
  • Don’t overdo it with styles: Take away any unnecessary and redundant styles.
  • With an effective call-to-action: Do you need all that information in your emails? It has always been part of best practices to direct subscribers away from their inbox and onto a landing page as quickly as possible.

Clipping emails will shorten your email campaigns

Besides delivery issues, file size is another concern. Sending large emails, for example, may result in truncated emails in specific email accounts. In Gmail and iOS environments, this practice is known as “email clipping”. In a clipped email, you can show your subscriber a preview of your campaign and request that they download the entire message.  

Undoubtedly, clipped emails are an engagement issue, not a deliverability issue. Your CTA is especially important when it is omitted from your edited campaign. Your subscribers will have to click an extra time to access important content.

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