Importacular allows you to determine what settings match the addresses in your data source to addresses on existing constituents in the Raiser's Edge (see this knowledgebase article for more information). We understand that the settings that are best for you will differ based upon your location and your data standards, but we do find some settings to be generally helpful.
For organisations in the UK and Canada, you may find that postal code is an acceptable matching criteria since postal codes in those two countries tend to be fairly specific. If it is not specific enough, you can add additional fields (such as Address Line 1, etc.) to make it more specific.
For organisations in the US, the zip code is set to only match the first five digits (since we recognise that many organisations have the four digit extension in RE, but most constituents will only provide the first five when filling out their address). As that five digit zip code can be a broad area, we would recommend pairing that with a minimum of the Address Line 1 (and generally the Address Equivalents as well to account for known abbreviations).
For more information regarding Address Equivalents, please see these knowledgebase articles: