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How does email size affect deliverability?

What could be more important for an email marketer than knowing their carefully planned email campaign is being successfully delivered and receiving customer attention?

Spam filters can make emailing difficult by requiring that special rules are followed before sending out an email campaign. The question, “How do I make my emails spam-filter friendly?” is quite common among email marketers.

There are many criteria to follow in order to avoid spam filters and get your email campaigns delivered. Is email size one of them?


At what point does email file size cause deliverability issues?

Email size plays a considerable role in email deliverability. Spam filters take email size as one of the criteria for marking emails as spam.

To put it more plainly, how many KB can you send in an email and still avoid it ending up in the spam folder?

If you are wondering how many KB you can send in an email, keeping it under 100 KB increases the probability that you will stay out of the spam box. However, exceeding the email size limit by even a few bytes will make a difference.

Take this into account if sending emails to:

  • Apple Mail (5, 6, 7)
  • Outlook (2007, 2010)
  • Google Apps
  • Yahoo!
  • AOL
  • Gmail

One byte more than 100KB will probably cost you a trip to the spam folder.


How can I avoid email deliverability issues before they happen?

In order to ensure that your emails get delivered to your subscribers‘ inbox and not trapped in spam filters, keep your emails short, clear and to the point. Remove all unnecessary photos, attachments and other components that may slow down the loading time and increase the size.

Keeping the email size under 100 KB is not just a baseless rule. There are other advantages to making your email light, for example, shorter loading time.

If the email consists of large and heavy images, the loading time will increase. The loading speed of your email campaign on devices using data, such as mobile phones and tablets, will be slower than on a desktop.


Keep your email size in check

At this point, marketers may ask, “How do I know the size of my email?”

An email‘s size is due to its components, including the basic email template and all necessary text, images, links and attachments.

Marketers designing their campaigns are well aware of the size of images and attachments because often they are in charge of making or adding them.

It is more difficult dealing with text and links. The size of text varies not only according to the length but also the size of the characters, their color and other formatting options.

If your email marketing provider has an email size checker tool, make sure to use it before you send your campaign to your audience.


Choose the right image sizes

Now that you know how many KB you can send in an email, here are a few simple rules you should follow when working with different email components.

There are three golden rules for using an image in an email:

1. The safest email size limit (images included) is less than 100 KB

This is like solving a simple math equation. No matter how large or how many images, as long as the whole email message size is less than 100 KB, you should be safe.

To help follow these principles, emails sent using many email marketing platforms don‘t actually include images, but they are loaded from our server on an individual recipient‘s computer when an email is opened.

2. Use .png format instead of .jpg for your images

The .png format allows you to optimize images by making them lighter without a change in quality.

3. Never put a single image in your email without any text

Spammers usually use large images as a text container, because bots and programs that check content cannot read images. If your email contains only images without any text, your campaign will most likely land in the spam folder. We suggest you use proportions of 50/50 or 60/40 text to image.


What about attachments?

Large attachments will be recognized as potentially harmful by many email providers like Gmail, and therefore could land a message in the spam folder. If you decide to use attachments in your email, make sure the size of each attachment is no larger than 2 MB, and the total size of attachments is no more than 10 MB.

We suggest avoiding attachments altogether, using links to stored files or special landing pages. Motivate your subscribers to click in order to increase your CTR (click-through rate), website visits and brand awareness.


Conclusions for greater deliverability

Spam filters are often misunderstood as an aggravating obstacle for reaching a customer, yet their only aim is to improve email quality all over the world. Make your emails clear, straightforward messages, removing unnecessary spacing, attachments and other components.

We want to remind you that email size has an impact on email deliverability, but we don‘t want to stress you out by trying to squeeze your creative email campaign into 100 KB just out of fear of spam filters. Keep your subject line, email content and links clear, avoid spam words and send only permission-based emails.

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