[tsimionescu]

So Postfix does about 1/10th of what Exchange does, and is secure. Very well, do one thing and do it well.

You talk about composing it with other stuff to create a system, but fail to mention if that system will still be more secure than Exchange. Even if each component of the system is individually very secure, that still doesn't tell you much about the security of the system. It's extremely easy to piece together two secure components and obtain 0 security.

Edit: accidentally said 'not secure' instead of 'secure' in first statement, completely changing the meaning. Corrected in-place.