These definitions may be helpful however as you mentioned an SOP on Clinical Trial Communications is key. Include info on training to the definition, when and how to file in the TMF, how to use a central repository etc.
Communications – Relevant
Communications/correspondence that document agreements or significant discussion regarding trial administration, protocol deviations, trial conduct and adverse event reporting.
Communications – Non-Relevant
Ephemeral documents, defined as documents of trivial nature and therefore not business critical or only of short term value i.e. an email invitation to a meeting. These types of documents have little or no value as a record of compliance.