It is recommended that when you are sending an e-mail to a group, you do not attach a document but rather link to the document you wish to share. There is a file size limit on e-mails, typically anywhere from 10 to 25MB, depending on the e-mail service. When sending an e-mail to a listserv, that file size limit is much smaller - less than 1 MB.
This how to video takes you through three different options: