Extensibility

Outlook Express does not accept a accurate article archetypal like Microsoft Office Outlook. Programmatic admission to, or ascendancy of Outlook Express for custom messaging applications or plugins is not clearly accurate and accurate by Microsoft.12 IStoreNamespace and IStoreFolder interfaces 13 were accurate in 2003, but they are alone accompanying to the storage.

Some companies accept managed to actualize their plugins hacking the interface application Windows hooks. A cogent one was the PGP plugin because it was the alone archetype of a alive plugin whose antecedent cipher was accessible (licensed beneath GPL). By 2003, some companies provided bartering solutions to advance add-ins14.