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A Definitive Guide to Email File Size

As an email marketer, the urge to include every conceivable thing in your email template in a bid to leave your subscribers utterly delighted can get very hard to overcome at times. But betray that temptation you must, for the weightier your email gets, the greater the number of issues you’ll have to deal with. 

For starters, emails having bigger file sizes will have higher loading times. And, that’s a surefire recipe of disaster, as we all know. Irrespective of an individual’s attention span, no one likes waiting an eternity for their email to load. Then, there’s the threat posed to email deliverability; larger emails trigger spam filters which can ultimately keep your emails from reaching your subscribers’ inboxes. Overall, if your file size isn’t regulated, your campaign’s engagement and eventual success stands to be adversely affected. So, to help you stay on the right path, in today’s blog we give you the low-down on email file size, and share some actionable tips that will allow you to optimize it. Read on to find out more!

What Contributes to the File Size of an Email?

Now before we dive into file size optimization measures, at the outset it is important to have clarity regarding all the elements that add to an email’s weight. They are:

  • The HTML code of the email.
  • The images present in the template.
  • The number of frames in your animated GIF.
  • The kind of custom fonts in your email.
  • The files you add as attachments. 

There are two fundamental limits that you must take into account while curating your Salesforce email templates:

  • Your email system’s limit to send a message.
  • Your recipient’s email system’s limit to retrieve a message.

So, if you happen to send an email whose file size is within the limits of your mail system but exceeds that of your recipient’s, it’ll never reach them. For greater clarity, we have listed below the sending and inbound size limits of some popular email clients.

  • Gmail- 25 MB
  • Apple Mail- 20 MB
  • Outlook- 20 MB
  • Yahoo- 25 MB
  • AOL- 25 MB
  • GMX- 50 MB
  • Proton Mail- 25 MB
  • Zoho Mail- 20 MB
  • Thunderbird- no limit

Next, let’s take a look at the sending size limits of some popular ESPs.

  • Mailgun- 25 MB
  • Sendgrid- 30 MB
  • AWS SES- 10 MB
  • Postmark- 10 MB
  • Mandrill- 25 MB

To err on the side of caution, most experts recommend keeping email file sizes under 10 MB. However, it is not necessary to treat this number as the “ideal” file size. As a matter of fact, no figure can be given that status. What you deem ideal for a region with better internet infrastructure, will not hold true for another where the infrastructure is not as sophisticated. 

According to Litmus, the average email file size of a non-mobile optimized email is approximately 2.3 MB, and that of a mobile-optimized email, nearly 2.8 MB. While at first glance it might seem a little odd to consider that a mobile-optimized email would be heavier than a non-mobile optimized one, it makes perfect sense if you actually think about it. You see, to optimize emails for mobile, more code is required, which contributes to this additional weight. 

Measures to Optimize Your Email’s File Size

Since the SMTP protocol stipulates no message body limit as such, many tend to overlook the body size of their emails. This, of course, leads to such parties inviting the wrath of spam filters down the road (in the list of most common anti-spam rules, size-related points find mention at the very top). Typically, it is observed that message bodies exceeding 100 KB end up triggering spam filters. Hence, senders are generally advised to keep their email body size in the range of 15- 100 KB.

Besides inviting an unenviable spam score, emails with large file sizes also bring rendering issues to the table. Most email clients will only partially render a large email body, leading to subscribers viewing your email in bits and pieces; no points for guessing what kind of a taste such an experience will leave in their mouth. 

Another terrible consequence that sending large emails invites is that of email clipping, a condition native to iOS and Gmail environments, wherein the subscriber is shown a truncated version of the email in their inbox. In Gmail, if your email size exceeds 102 KB, only a partially-rendered version of it would be shown to the reader. In order to access the whole email, they would have to click on another link (which is barely noticeable) in the email. 

To steer clear of all these issues, thus, consider adhering to the following size optimization best practices:

  • Always aim to keep the images in your Salesforce email template under 200 KB.
  • Remove redundant styles, unnecessary spaces, and unhelpful comments from your email code. 
  • For large attachments, rather than adding the file itself, add a link to it in the email.

Wrapping It Up

A lot of hard work, time, and resources go into curating an email campaign. All of it stands to go in vain if your email templates are found flouting the file size norms. With the insights offered above, we hope you have the necessary clarifications to keep your email file size just right.



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