Select Search Letters or Search People to access the search function: then add filters depending on what you want to look for.

Use Search Letters to get a list of letters which include specific content words, have been written in a specific year, and/or are addressed to specific recipients: for this you need the recipient ID, which can be found in the correspondent metadata. For example, Richard Berenger’s ID is found by going to Correspondents > Richard Berenger > scrolling down to Berenger’s Personal Information and Person ID.

If you want to find references to people (recipients or any other), the easiest way is to select Search People and search for names.