You can configure imapproxy for @Mail to improve performance. Just do the following:

1.) download imap proxy from: http://freshmeat.net/redir/imapproxy/35569/url_tgz/up-imapproxy-1.2.4.tar.gz

2.) untar, install:

% tar xvfz up-imapproxy-x.x.x.tgz
% cd up-imapproxy-x.x.x
% ./configure
% make && make install && make install-conf && make install-init

3.) If the installation is successful, edit your /etc/imapproxy.conf file. Find:

server_hostname localhost

4.) change "localhost" to your server's hostname, if necessary. Then, find:

listen_port

5.) change this to:

listen_port 143

6.) then find:

server_port 144

7.) change this to:

server_port 144

8.) afterwards, open up /usr/local/atmail/mailserver/etc/imapd. Find:

PORT=143

9.) change this to:

PORT=144

10.) Restart the services:

% /etc/init.d/imapproxy stop
% /etc/init.d/atmailserver restart
% /etc/init.d/imapproxy start

This will then run your IMAP port through a cached proxy.

The configuration for Exim's outbound SMTP port might be a bit daunting, so here is an easier example that you can do via iptables. It routes any outbound traffic from port 25 to a port you want. For example, if you wish to route to port 465:

 iptables -t nat -A OUTPUT -p tcp  --dport 25 -j DNAT -- to-destination :465

This is particularly useful for instances where you need to route SMTP traffic to another port due to ISP limitations.