Cannot Receive the Contents of a Mail Drop

Mail Drop does not work for me. I seem to be able to send large attachments but they do not download. Example: a 500mb .MOV file will get sent and then will appear in the 'In Box' of the received email account with the icon of the .MOV attachment. Beneath the icon there is a dynamic indication of the amount of data being downloaded. But the numbers don't go above 100mb and then the whole thing chokes off leaving a greyed out icon that returns to 0. I have tried this with large folders of photos as well. Always get the same result. Any ideas would be most helpful.