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What is the maximum file size an email attachment can be?

The file size limit for email attachments on the Cantab service is 25MB.

The main reason for this file size limit is security - without these limits it would be possible for malicious users to bombard email servers with huge email attachments and ultimately crash the servers. Even if we were to increase the file size limit on our end, there is no way of ensuring that a recipient's server would accept a file of that size.

If the file attachment size is too big, and thus rejected by the recipient's server, you will usually be notified with what is known as a "bounce" message; these exist primarily to inform users that their email has not been received, and provides a brief reason why.

Should you wish to send a file to a recipient that is over 25MB in size (or has otherwise been rejected by their mail server) there are two alternatives available that would allow you to work around these limits:

- Using a cloud storage or FTP link (a solution such as Dropbox, Google Drive, etc.) can provide users with a link to download the file, this can then be inserted into an email.

- Using file compression software (such as Winzip, or the native functionality built into most operating systems) to make the file smaller for the purposes of attachment.