Several ISP's and hosting companies place restrictions on the size of individual emails that can be received and sent though their servers, we have a limit of 30MB per email however please note we also have no control over such restrictions elsewhere.
As a workaround, customers are advised to create an FTP login via their eXtend control panel and upload the file attachment to that location. Customers can then simply email the recipient those FTP details, and they can then download the file via FTP using the login you created.
As another suggestion, some versions of Microsoft Outlook (and Microsoft Outlook Express) support an option "break apart messages larger than (some size)". Setting this to say 1MB is often appropriate, but this is only useful if you know the recipient also uses Microsoft Outlook or Microsoft Outlook Express (in which case their mail client will re-combine the email).