Email rejected: message too big

First of all, it is worth mentioning that email is not really suitable for sending large files.

When you send an email with an attachment, there are a number of limits that can cause your email to be bounced (rejected) as “undeliverable”. These are the maximum message size of the sending party, the maximum message size of the recipient and, finally, the size of the recipient's mailbox (which may also be full, for example).

Every email message passes through the mail server of the sender and of the recipient. To be sent successfully, both parties must apply a limit that is larger than the message. Most servers have limits set on the maximum size of an email. This includes the attachments plus the message itself (including things you do not see yourself). The vast majority of mail servers apply a limit of 20MB per message. An attachment of 20MB will certainly not work, because a (binary) attachment has to be encoded before it can be sent (using the so-called MIME format in which emails are sent). This increases the size of a message by at least 20 to 30%. In practice, this means that with a 10MB limit you can actually only send an attachment of about 7MB. We apply a limit of 20MB, which means the maximum size of an attachment is around 14 to 15MB.