Mr Sam, My self and and many other have had problem with the one-TAB format. It would be interesting to learn if there are any particular reson for this format.
There isn't. The format is designed to be machine-parseable with ease, and machine-generatable. It is meant to be used in conjunction with custom, site-specific management tools.
As a reference example, consider webadmin. It provides the ability to create most common smtpaccess entries, from a simple web-based form. After webadmin updates the smtpaccess file, makesmtpaccess is invoked automatically.
Manual editing of smtpaccess is not required. You should not need to edit smtpaccess directly, unless you're doing diagnostics or debugging. As such, the question is moot.
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