Connections to EWS stops when states reach above 5000

[watz]

hello Team
I have a pfsense installed on hp dl380 gen6 , 49 gig ram , and on a 127 gig hard drive .
We using hosted exchange , and the issue i have is mainly with MAC Outlook users , accessing emails on Exchange Web services from our email provider.

State table currently is 0% (3311/4910000)  , however should it go above 5000 , then outlook starts to drop connections . Emails stop coming and mails can not be sent . I have to continual reset the states to allow mails to come and be sent . This can be as much as every 2 hours .

On the firewall rules .
I have allowed all the ip addresses of my exchange provider to pass through
On the Wan
IPv4 * Exchange provider ip  * WAN address * * none  
On the lan
IPv4 * * * exchange provider ip * * none

I have rebuilt the firewall twice , incase i was missing something .
port 443 to every other email provider works ie gmail ,yahoo ,

Your help will be be appreaciated .