I have an issue with my Debian Postfix mail server running Roundcube for webmail. When web clients receive an attachment over 900K in size, they cannot open the email message. They get an "Internet Explorer cannot display the webpage" error if using IE, or just a blank page if using Mozilla Firefox. If they use an IMAP client like Outlook to get their email then there is no problem with the attachments.
Has anyone seen this before and or know of a fix?