Email sizes are fundamental for a few important reasons. One is security, and another is the performance of your email. This article covers, in brief, all you need to know when it comes to email sizes, focusing mostly on email file size limits.

Why email size limits are used

There are three main reasons that there is a max email size set. And they are;

  • Performance : Email is not built to handle massive data transfers. They use SMTP, an old protocol. Most systems cannot process numerous data sources simultaneously. MTAs frequently analyze incoming data for malware and other threats, using resources and slowing system performance.
  • Storage database size : Store email data on a server (either cloud or local). That's why both the message and the inbox have restrictions.
  • Security : Email systems typically retrieve data via a restricted number of ports. This renders them vulnerable to DoS, Denial of service, attacks: a flood of massive messages can bring the system to a halt. This scenario is called an email bomb.

Your and the recipient's email capacity limits the maximum email size. When sending transactional or marketing emails to a large database of email addresses, you should avoid sending messages larger than 10 MB.

Things that affect max email size and how to optimize them

  • Embedded images and elements : Simple alerts frequently include visuals, if not your brand's graphics. Their sizes vary based on the digital form and how it is inserted. To optimize, link to images housed on external servers if possible.
  • Attachments : With attachments, it's simple. Max email body size is unaffected by the files attached. That number usually includes all attachments. Upload files to the cloud and include a link in your message.
  • Encoding : MIME-encoded (base64) messages increase email size by 33%. Remember this when developing multipart messages.
  • Other : Element-by-element, a message's Headers, signatures, and formatting all add kilobytes.

Things to consider about email file size limits

Spam score

Evading spam filters and addressing the recipient's primary folder is difficult in an email. There are no universal malware detection criteria. A round of dup "anti-spam" guidelines includes the size-related criteria.

The SMTP protocol has no text body restriction. Others have their own limitations.

Many operators' tests show a link between email size and deliverability. Messages of 100–150 KB body size usually trigger spam filters. So, maintain email body size between 15 KB and 100 KB.

Rendering flaws

Large emails also have loading and rendering times. Your recipients don't always have high-speed Internet connectivity; thus, a lengthy email loading procedure may irritate them. Also, huge email bodies may be partially rendered in many email clients, resulting in partial pictures or content clipping. This may negatively impact your customer's digital experience.

Despite the many limits and concealed restrictions, there are basic criteria for creating effective emails. First, reduce and optimize email body size.

SMTP Size limit errors

Here are the most typical SMTP mail size faults. There are two:

Error codeDescriptionReason and how to solve
Error 523The Recipient's mailbox cannot receive messages this big.Your message exceeds the size limit of your recipient's server. Check the size of the email body and attachments. Use the recommendations above to optimize it.
Error 552Requested mail action aborted: exceeded storage allocation or size of the incoming message exceeds the incoming size limit.The email box of your recipient is full. In this case, you have nothing to do: your recipient should clean up his or her inbox. Or your message exceeds the limit set by the administrator. Check the size of your message and optimize it.

Perfect email rules

Considering the above constraints, we've devised a quick email size optimization checklist. Here are the guiding principles for creating a list of max email sizes:

  • Keep email body size 15-100 KB.
  • Keep attachments under 10 MB.
  • Post your files to an external server and link to them online.
  • Use photos, GIFs, and other multimedia sparingly.
  • Remember that over 42% of emails are opened on mobile. Remember this when making email templates. They must respond.

Bottom line

Now that you know the fundamentals of max email sizes, you now understand why some emails might not go. You are also better positioned to know how many MB you can send via email and why there is that limit.