While I had a full Cargo (10 items) I clicked on an email to receive an attachment and received the default message:
“Mail Attachment Collected! You have collected “500X” from the email. This has been placed in your ship.”
Of course, the item was correctly NOT collected as my ship’s cargo was full. So there just needs to be a default message for this case, such as:
“Your ship’s cargo is full. Unable to receive email item!”
PS Really enjoying your game. Nice job.