Sending large email messages (or large attachments)

Our servers, like all others on the Internet, limit the size of a message you can send, and that limit includes any attachments. Our limit is 25 MB, and we aren't aware of any large site that has a larger limit.

Due to the way email is encoded when being sent between mail servers on the Internet, attachments have an even smaller practical limit. Encoding increases file size by a factor of 1/3, so the actual limit for non-text (including, for example, photos and video) is 18.75MB. Convention (BASE64 maximum line length) dictates further restrictions on the encoding which reduces the real limit to something bewteen roughly 18.14 and 18.29MB, depending on the mail host.

Since all email includes headers, the actual maximum size of attachments in an otherwise empty message will be a few KB less.

If you need to send a file larger than that, you have a couple of options.

Make the file available on the web

Depending on the type of file, there are a number of sites which will handle the hosting for you (e.g. YouTube for video files, Flickr for images, Google Docs for nearly everything else, etc.). Be aware that some of these will have public availability as the only option, and thus not be your best options if confidentiality is a key consideration.

If you have a Panix shell account, you can create a directory in your web space to host the file(s) and provide the URL for that space to your correspondent in email.

If the data is sensitive, you can protect the directory with .htaccess and .htpasswd. Detailed instructions can be found in our Web FAQ.

Split the file

There are tools for PCs and Macs that let you split a large file into multiple parts, often with compression. This will allow you to send the file via multiple emails; the recipient would need a similar tool to merge the parts back into a single readable file.

Depending on the size of the file, this method can be somewhat time-consuming.

Here are a couple of programs that can segment and recombine large files on Windows and MacOS. There are many many more.
WinRAR (Windows, Mac)
Keka (MacOS app store, $5)
Keka (home page, link to free download in small type)

Last Modified:Tuesday, 19-Sep-2023 12:50:01 EDT
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