Email size limits

We use emails for most of our day-to-day communications. While using emails, you should keep in mind that every email sending provider has a maximum limitation on the size. You should keep this in your mind and compose your emails.

Why is there a maximum size on the emails?

Here are some considerations when sending emails.


Email systems are not in a position to transfer a large volume of data at a time. In fact, the functionality of email systems is based upon SMTP protocol, which is relatively outdated. Most email systems are not in a position to process multiple data sources at a given time as well. If the email size is too big, it will create a direct impact on performance.

Storage limitations

All emails you send and receive are stored in servers. There is a storage limitation in the servers as well. This is another reason why email providers have implemented a maximum file size limitation


Email systems are using a limited number of ports to receive data. Otherwise, they will be subjected to DDoS attacks, which can bring down the entire system.

What is the optimum size for an email?

At the time of composing an email, you should keep the email attachment size limit in mind. For example, assume that you are sending an email to a recipient, where the email provider has a limitation of only 10MB per mail. Hence, you should make sure that you are not sending an email with attachments exceeding 10MB. The most popular email providers, such as AOL, Gmail, and Yahoo are supporting 25MB for each incoming and outgoing email.

Should you always optimize the size of your emails?

Yes, it is important for you to always optimize the size of emails that you are sending out. Otherwise, there is a possibility for your mail to get filtered by spam filters. Even if the email attachment size limit is 20MB, you shouldn’t fully utilize 20MB. Instead, you should reduce the size as much as possible. The ideal recommendation is to keep the size of an email from 15 KB to 100 KB. Then you can reduce the chances of your mail getting trapped by spam filters. Large emails are often subjected to rendering issues as well.

How can you optimize your emails?

Attachments are responsible for the overall size of your email. Hence, it is important to keep the email attachment size limit in your mind when optimizing the emails. If there is a need for you to attach a bulky file, it is better if you can upload it to a cloud and then include the URL on the body of the email. This will help you to keep the size of the email low.

Likewise, you should take a look at the images and other elements that you embed on the email as well. If there are lots of images on the email, its size will increase.

MIME encoding can increase your email size by around 33%. If you are planning to proceed with encoding your email, you must keep it in your mind. On top of everything, you should understand that every single message element present in the emails such as formatting, signatures, and heading can contribute towards the overall size. You should keep this in your mind and carefully compose the email.

Final words

All the emails that you send should be limited to a size between 15 KB and 100 KB. You should never attach any files over 10 MB to the emails. Instead, you should upload them to a cloud and include only the URL. Likewise, you should also keep multimedia content low in the email as much as possible.