What are the size limits for emails?

Most mail systems impose two distinct limits that determine how large your email can be: one for the total message size and another for the message body.

The total message size is usually between 20 and 25 MB, covering the entire message including attachments. Since attachments are Base64 encoded, their size increases by roughly 33% during transit. A 20 MB file can easily exceed the limit once encoded, which often results in a bounce, the mail server rejecting the message outright.

These limits exist because SMTP was designed in the 1980s when storage and bandwidth were expensive. Early systems couldn't handle large files, and those constraints became baked into email infrastructure. Even today, servers enforce these limits to prevent resource abuse and keep mail flowing efficiently.

This is the equivalent of a cargo ship that exceeds the maximum load allowed at the port. If the ship is too heavy, the harbor master refuses entry until the load is reduced.

The message body limit is smaller and defined by email clients rather than servers. For example, Gmail clips any message body that exceeds about 102 KB of code (HTML and text combined). The message is delivered, but part of it is hidden behind a \[Message clipped\] link.

It is similar to a port authority only showing the first page of a ship's manifest and filing away the rest for review. The message still arrives, but the viewer sees only a portion of it unless they request the full version.

Best practice: To avoid size-related issues, send large files through cloud storage services like Google Drive, Dropbox, or OneDrive, and include download links in your message instead of attachments.