Another, considerably cheaper, method of using Exchange in a dial up environment is to take advantage of the services provided by no-ip.com, where you can download a utility that identifies your system to no-ip.com's web and mail redirectors for your domain. This means you can host your own web-mail and SMTP service without having to worry about fixed ip addresses.
For a low cost they can even reflect your MX connection so your SMTP operates though an unpublished, non-standard port, helping to prevent spoofing and attacks on the port, as well as a few other tricks.
This is a wonderful solution for SME's with dial up connections or DSL. With scheduled sial-ups you can even reduce the likelihood of attacks on your system by only allowing connections at specific times throughout the day. And if you really want to allay fears of attack, don't use your own domain. Take advantage of no-ip.com's second level domain service and hide your server away using a hostname crackers would find hard to guess.
And how do I know this works? I use it for my extranet, allowing me to keep clients up to date with the progress of their projects without filling up their office e-mail accounts and giving them the ability to communicate with other project team members quickly.
All in all, inexpensive, requires the installation of one small program that runs as a service and control of the redirection through an easy to use web interface.
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