Why does the upload attachment display the words "upload failed" and "information lost" when sending an email?

The upload failure may be caused by temporary network interruption, manual cancellation or name conflict. You can do it. If it fails, cancel it and add it again. If your attachment is too large (several meters in space), I suggest that you send it separately to avoid receiving your mail normally due to insufficient capacity of the other party's mailbox, which is also a way to avoid network interruption. If you still can't submit it again, you can copy and back up the contents of the email body first, and then go back and create a new email to send the test.