For: A venerable product that behaves extremely well and does exactly what it claims to do competently and smoothly
Against: Can become a bit pricey in large enterprises
Verdict: PGP continues to set the standard for pure email security in an enterprise environment. Our Best Buy.

PGP Desktop Enterprise is a suite of encryption products in a single package that includes email encryption. When you buy the product, the licence key activates the software for those features purchased.
Upgrading is easy. Simply purchasing the new features, for example whole disk encryption, causes a new key to be generated. Simply insert the new key in place of the old one and the product is upgraded.
There is no need to reinstall. In fact, we attempted a reinstall over a previous installation of whole disk encryption and the product refused our efforts with no damage to the existing installation.
The solution is simplicity itself to use. Once installation is complete, including a very simple key generation process, the product is ready to configure.
This is done through policies that dictate everything from the behaviour of the encryption and digital signing to the granularity of an individual recipient if desired. Broader policies are equally simple to implement.
For example, a policy to sign all email by default translates transparently to the user including caching the user's key at startup.
As one would expect from PGP, documentation is very good. There is a short but comprehensive quick-start guide and additional documentation is available on the website. There is a variety of support options for users of most types, from individuals to small businesses and larger entities. The support portal is quite complete.
With prices starting at £40 per user per year, PGP Desktop Enterprise Email v9.6 represents good value. However, for true enterprise use it requires PGP Universal Server at an additional cost, which then allows full corporate management of the entire PGP encryption suite.