When you send an email with an attachment, there are two types of size limit that can cause your email to bounce back as “undeliverable” – the message size limit of both the sender’s and recipient’s email servers, and the size limit of the recipient’s inbox.

Every email message goes through both the sender’s email server and the recipient's email server. A successful delivery would require the size limit of both email servers to be larger than the actual email message. Most servers have file size limits (counting both the message text and attached files), and this is almost always less than 20MB.  A bounce could also result from the email message maxing out the recipient's mailbox. Any email attachment (binary file) has to be encoded using the MIME format in which emails are sent, which increases the size by 20-30%.  This means, with a 10 MB size limit, you can actually only send a file that is around 7 MB in size.

Below is a list of size limits for major email service providers.

Note: 10 MB is the typically used size limit for email servers other than the web-based mail services listed above.