The guiding principles for determining whether or not to build content in a wepage vs. a document is the same for determining what to include in an e-mail vs. a document, whether that means a text e-mail with either an uploaded and attached PDF or other document or an e-mail with links to webpages.
It's best to use e-mail together with links to webpages with more or supporting content to the e-mail. If a webpage doesn't exist to link to, create a webpage first and then compose an e-mail with some teaser copy and a link to the webpage with the complete content. Additional things to consider have to do with the limitations of composing e-mails vs. documents or webpages:
Group Communications to Members While Developing Documents
Development of content for either print or electronic distribution often occurs in groups or committees of individuals who commonly team-develop and collaborate on documents for broader distribution once versioning is finalized. Sharing content over electronic media can be done by confining documents that are not yet accessible to members over e-mail or by keeping webpages in an unpublished or working state.
In these situations it's best to make sure everyone involved understands the significance of accessibility in choosing the design and layout of the content, particularly if it's intended to be broadly distributed electronically and made available to university audiences and the public at large once the content is finalized.