Attachments less than the 10 MB configured limit are not deliverable

The message limit is a total maximum for the entire transmitted email: the message body, message headers, all attachments, and encoding, which in some cases can expand the size of the email. For example, depending on the encoding and the content of the email, an email with an 8 MB attachment could easily exceed the transmitted message size limit of 10 MB.

Therefore, attachments should be significantly smaller than the configured limit.