Why do Emails have a Size Limit?

3 minute read

Emails are a popular method of communication in this technological world we live in. They provide us with a reliable system for communicating with friends, family, colleagues and companies. I’m sure that like me you at some point in time you have attached files to an email. You may have sent or received anything from holiday photos to invoices – files are files. I’m sure that most of us (if not all) are aware that you can “attach” files to an email. Emails obviously have the functionality needed to send files. However, emailing is not designed nor intended to transport large amounts of data.

Recently I have had an increasing number of incidents where people have had issues either sending or receiving emails with large attachments. As such I decided to write this article to explain what is going inside the email system.

What is the issue?

No matter whether you use Outlook, Thunderbird or another platform to send and receive email they all use the same protocols. There are three common protocols for email systems, IMAP, POP3 and SMTP. The latter – SMTP, stands for “Simple Mail Transfer Protocol” and can be easily remembered as “Send Mail to People”. SMTP is used for sending emails as you may have guessed and has been around for many years. As with all other technology it has advanced tremendously as is the same for the expectations of it. Unfortunately, it never has been designed nor intended to handle massive amounts of data such as large or multiple attachments despite common belief.

Basically, larger emails cause a greater load on the systems which transfer the email. This is more of an issue when you realise that emails pass through multiple servers on their way to the recipient(s). Here’s a list of the main downsides to sending large emails:

  • Mail servers give larger emails a lower priority which will cause a higher delay
  • Spam filters will often reject large emails.
  • The mail server of the recipient may have a smaller limit than your sending server – the email may not be delivered.
  • Larger emails will use the space on your account quicker (Believe me, it soon adds up!) This will also slow down your mail client.
  • Emails will take longer to send and receive (Broadband speed still isn’t great)

Please note that the limit applies to the entire email (text, headers, attachments etc. combined) and not just attachments.

What are the common limits?

Generally, the limit for both sending and receiving (yes, there is a limit on receiving too) is 25 megabytes. It is worth noting that the limit for sending and receiving can differ from each other. There is of course the odd one which has a different limit but can’t much due to the reasons I listed above. I have seen some providers who set their limit to 10 MB and by default the Microsoft email system (Exchange) which many companies use is set to 10 MB. There are others which use 25 megabytes and even some with a limit higher than that.

What can I do if I need to send something larger than one of these limits?

I would always recommend using a service such as Dropbox, OneDrive, Google Drive or similar for sending files larger than 20 megabytes. Most cloud storage providers will give you a small amount of storage space for free. All you need to do is sign up with one of these services, upload the file and insert the link in the email.