Deepness doesn't really matter, key point is findability. Citing Morville findability is:
- The quality of being locatable or navigable.
- The degree to which a system or environment supports navigation and retrieval.
- The degree to which a particular object is easy to discover or locate.
To this definition you should add some desirable properties (also from Krug's take about easiness):
- Memorability. I need an easy way to remember search for my stuff (unless I already know where it's located, in this case I need an easy way to memorize this information).
- Navigability. I need an easy way to explore content and its organization.
- Flexibility. I need an easy way to change or extend how I organized my things.
After this introduction the question you should ask yourself is if same element (e-mail template, in your case) may stay in different folders or tagged with multiple tags. Think about your own question on UX: it's tagged with tags and folders.
Will you have an e-mail template tagged
update? Will you also have an e-mail tagged
confirm? If your answer is yes then go with tags, they're not harder to understand because now widely used (also I don't remember which OSX version (re)introduced them starting again this battle) and you'll get the kind of flexibility you need.
If you can have multiple tags you will:
- Be able to perform more general queries: show me all e-mails about
- Be able to perform complex queries: show me all e-mails about
partners written in
Same result is hard to perform using folders (unless they're just an implementation detail and users aren't aware of them). From a more technical point of view folders won't give you the ability to - quickly - scan/search for attributes (unless you keep an index as many OSes do for your file system) and links are harder to implement. Tags let you free to use best storage option (database, multiple folders with any arbitrary subdivision and so on).
If you do not have multiple tags and you have only one level of deepness then folders/tags metaphor are equivalent (from user point of view) but if you already organize your application to use tags then you'll be ready for future changes (maintainability).
Regardless deepness hierarchical organization can be done as a special case of tagged organization with magic tags:
subcategory:privacy. Same element may even appear in multiple places. This is, for example, what it's done in big stores to organize their products: think about Amazon, products are tagged but you can search for tags or navigate using a hierarchical organization.
More specific example about your context.
Imagine you have these e-mails:
- Privacy update for customers. Shared between Customer Care team, sellers and layer. Available in five languages.
- Privacy update for partners. Shared between R&D, office for payments, layer. Available in five languages.
- Request for a quote. R&D and Technical Support. Available in two languages.
- Request for information (customers): Technical Support, management. Available in two languages.
- Request for information (partners): Technical Support, R&D. Available in two languages.
One level hierarchical organization won't give you the ability to quickly scan these few e-mails unless you already know where things are located (and it may not be obvious), in your case you have hundred(s) and people will soon ask for a bookmark feature to keep track of what they use most...