mail only downloads headers of emails with large attachments

Hi-

I have Maverick.

My mail is delivered though an Exchange Server.

At present emails download fine UNLESS they have a large attachment.

If they have a large attachment, the email will appear in the central "preview" pane with the address of the sender and the subject line, but will otherwise not download.

The email will only start to download once I click on the email in the preview pane. This can be laborious if I have 50+ emails with large attachments.

How do I configure mail so that it will download the emails, irrespective of the size of the attachments.

Thanks,

Richard