BT blocking incoming emails with attachments

The other day I emailed a document (with a .docx extension) to a address. It did not arrive, I did resend it but it still
vanished although emails with no attachments or other types (e.g. .pdf) get through OK.

The problem has been solved - my associate has now set up an address with one of the many webmail providers and that is working OK, but I
would be interested in knowing whether this problem is widespread with BT's email system.