Hello mat290,
Thank you for using Apple Support Communities.
We understand that you use iPad Notes to scan documents and then send them via email. After scanning and emailing, you delete them from Notes. You are now getting a message saying "Maximum attachments reached". When you delete the scanned document, do you erase it from the Note or do you delete the Note itself? If you just erase the contents of the Note, but leave the Note, the system may still be counting the attachments to the Note. Instead, try deleting the note after sending the document and create a new Note for the next scanned document.
Let us know how this goes.
Best regards.