Resources Hub » Knowledge base » How Does Email File Size Affect Send Time?

The effectiveness of an email marketing campaign depends on many factors. Marketers need to curate the copy, design the content, consider personalization, and craft the perfect CTA.

Something often not considered is how the email file size affects send times. If the design and curation process doesn’t factor these in, the campaign may suffer.

What is the email file size?

Every email file comes with a size (also called weight) that influences how the client handles the content. The file’s weight depends on both the HTML included in the message and the images, videos, or audio files it contains.

HTML code contains the meat of the images and videos for this email message.

Source: Campaign Monitor

The HTML code is the main weight of the email, while the loaded email weight refers to everything else the message requires for rendering. With the vivid and responsive designs available today, knowing the impact different weights have on the campaign is essential.

Keep in mind that 41.5% of marketers said that graphics are the most engaging type of visual content.

How to measure email file size

Email service providers measure email file sizes in kilobytes (kB) or megabytes (MB). The HTML weight of the email will be in kilobytes and the additional content (that includes the HTML) measured in megabytes.

Email clients don’t have a standard set of rules for handling larger file sizes.

Marketers should design their content according to the clients their subscribers use. This makes testing designs of the utmost importance before sending out a visually rich campaign.

For instance, Gmail will clip any message where the HTML portion exceeds 112 kB, but will allow sending a total email weight of up to 25 MB.

How does email size influence send times?

The size of the email doesn’t necessarily influence the send time at today’s internet speeds but does increase the amount of time the email takes to render.

The file size can also affect the email client’s ability to receive these emails. Because every client handles file sizes differently, it’s important to test the content before sending.

Another consideration is that the larger the email, the longer the load time will be, and the more likely it is that readers will delete the message.

Subscribers are also more likely to open emails on mobile devices, which means larger emails may end up costing them more in data charges.

Some best practices to optimize content for smaller file sizes include:

  • Use 72 Dots per Inch (DPI) for all images.
  • Design all images in RGB and not CMYK
  • Keep image sizes between 600 and 800k.
  • Choose the right image format appropriate for the content.
  • Include Alt-text for images as some client’s block all images from loading by default.

Does it really matter?

It takes a lot of time and effort to build your subscriber lists. If you’re not optimizing for the best experience, no matter the client, then you’ll probably see an increase in unsubscribe rates.

By conducting regular tests and checking how long every email takes to load, you’ll probably also see higher click-through rates and better engagement.

Rich and responsive content remains the most effective email marketing strategy. Dynamic and personalized email campaigns increase click rates, while journeys will improve the overall conversions.

However, that won’t work if the email’s HTML isn’t limited to below 100 kB, as some clients may then clip it. This is devastating if you consider the fact that you only have a few seconds to engage readers once they open the email.

What now?

It’s essential to optimize email sizes to improve engagement and conversion rates as well as help ensure that your emails get delivered.

Showing that you value your list members will go a long way to ensure you build their trust.

As HTML emails continue to enable greater email designs, testing for every possible outcome should be a priority for every email marketer.

If you don’t already have one, read this blog post on why a preflight checklist is vital before sending out any campaign.

This blog provides general information and discussion about email marketing and related subjects. The content provided in this blog ("Content”), should not be construed as and is not intended to constitute financial, legal or tax advice. You should seek the advice of professionals prior to acting upon any information contained in the Content. All Content is provided strictly “as is” and we make no warranty or representation of any kind regarding the Content.

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