all of a sudden my microsoft outlook email acct is not recieving emails with attachments

Any idea why my microsoft outlook email acct suddenly won't accept any emails with attachments?  I don't get any kind of error message. I would not have even known the email was sent to me except it came to my iphone.  Fourtunately I have a backup gmail account for my emails and was able to forward the email to my micosoft outlook email to print and file.  HOW do I get this fixed? Why on earth does the outlook email acct suddenly not allow my emails with attachments to come in???