Searching the content of a lead or thread isn't yet available; however, when you search for a contact, you can then see the conversation history associated with that contact.
Search for a contact
From Inbox, select the + button. A modal opens to search across existing contacts.
Type the name or number of the contact. The contacts that match are filtered in the list below.
Select a contact. You navigate the open conversation for that contact. If no conversation is open, a new conversation is opened.
View the contact details in the thread. At the end of contact details there will be a contact history with links to threads other than the one selected.
Note that the conversation history is also available when viewing a contact from the Contacts section of Leadferno.