Email size blocking allows administrators to set email size limits for both inbound and outbound emails. This applies to the full aggregate size of the email and any attachments. Any emails that exceed the specified size are rejected. If there is no maximum email size limit, the appliance would risk being bombarded with very large emails, causing it to stop working properly.
The Email Security - Server appliance accepts any-sized emails. The analysis engine by default analyzes emails that are 35 MB or less because many enterprises tend to block larger email message sizes.