My recommendation is to avoid emailing large files altogether. There are too many variables (both on the sending and receiving side) to guarantee delivery to a mobile device (often treated differently than a desktop).
Instead get a cloud file service like DropBox or Box.com. You can install a syncing app (usually free) on your computer (or work if the boss allows), or use the web interface to upload the file.
On the iPad you can use the (usually free) app and download the file without opening mail.
If you do need to email the file, you can generate a share link via the app (computer or iPad) and mail that link instead. This is nice for the recipient, since the email arrives promptly (because it's not huge), and they can choose when and where to download the file.
I realize this is not the answer you were looking for, but it is best practice (in my opinion) for larger files, and a pretty good practice for smaller ones too. Especially if you might need to email, share, or access them on the iPad them more than once (but don't want them taking up space in the between times).
