diff --git a/email/pardot.go b/email/pardot.go
index 1d1c7299a..421bb57b9 100644
--- a/email/pardot.go
+++ b/email/pardot.go
@@ -18,10 +18,12 @@ const (
 	// tokenPath is the path to the Salesforce OAuth2 token endpoint.
 	tokenPath = "/services/oauth2/token"
 
-	// contactsPath is the path to the Pardot v5 Prospects endpoint. This
-	// endpoint will create a new Prospect if one does not already exist with
-	// the same email address.
-	contactsPath = "/api/v5/objects/prospects"
+	// contactsPath is the path to the Pardot v5 Prospect upsert-by-email
+	// endpoint. This endpoint will create a new Prospect if one does not
+	// already exist with the same email address.
+	//
+	// https://developer.salesforce.com/docs/marketing/pardot/guide/prospect-v5.html#prospect-upsert-by-email
+	contactsPath = "/api/v5/objects/prospects/do/upsertLatestByEmail"
 
 	// maxAttempts is the maximum number of attempts to retry a request.
 	maxAttempts = 3
@@ -60,7 +62,7 @@ type PardotClientImpl struct {
 	businessUnit string
 	clientId     string
 	clientSecret string
-	contactsURL  string
+	endpointURL  string
 	tokenURL     string
 	token        *oAuthToken
 	clk          clock.Clock
@@ -70,7 +72,7 @@ var _ PardotClient = &PardotClientImpl{}
 
 // NewPardotClientImpl creates a new PardotClientImpl.
 func NewPardotClientImpl(clk clock.Clock, businessUnit, clientId, clientSecret, oauthbaseURL, pardotBaseURL string) (*PardotClientImpl, error) {
-	contactsURL, err := url.JoinPath(pardotBaseURL, contactsPath)
+	endpointURL, err := url.JoinPath(pardotBaseURL, contactsPath)
 	if err != nil {
 		return nil, fmt.Errorf("failed to join contacts path: %w", err)
 	}
@@ -83,7 +85,7 @@ func NewPardotClientImpl(clk clock.Clock, businessUnit, clientId, clientSecret,
 		businessUnit: businessUnit,
 		clientId:     clientId,
 		clientSecret: clientSecret,
-		contactsURL:  contactsURL,
+		endpointURL:  endpointURL,
 		tokenURL:     tokenURL,
 		token:        &oAuthToken{},
 		clk:          clk,
@@ -140,6 +142,19 @@ func redactEmail(body []byte, email string) string {
 	return string(bytes.ReplaceAll(body, []byte(email), []byte("[REDACTED]")))
 }
 
+type prospect struct {
+	// Email is the email address of the prospect.
+	Email string `json:"email"`
+}
+
+type upsertPayload struct {
+	// MatchEmail is the email address to match against existing prospects to
+	// avoid adding duplicates.
+	MatchEmail string `json:"matchEmail"`
+	// Prospect is the prospect data to be upserted.
+	Prospect prospect `json:"prospect"`
+}
+
 // SendContact submits an email to the Pardot Contacts endpoint, retrying up
 // to 3 times with exponential backoff.
 func (pc *PardotClientImpl) SendContact(email string) error {
@@ -156,7 +171,10 @@ func (pc *PardotClientImpl) SendContact(email string) error {
 		return fmt.Errorf("failed to update token: %w", err)
 	}
 
-	payload, err := json.Marshal(map[string]string{"email": email})
+	payload, err := json.Marshal(upsertPayload{
+		MatchEmail: email,
+		Prospect:   prospect{Email: email},
+	})
 	if err != nil {
 		return fmt.Errorf("failed to marshal payload: %w", err)
 	}
@@ -165,7 +183,7 @@ func (pc *PardotClientImpl) SendContact(email string) error {
 	for attempt := range maxAttempts {
 		time.Sleep(core.RetryBackoff(attempt, retryBackoffMin, retryBackoffMax, retryBackoffBase))
 
-		req, err := http.NewRequest("POST", pc.contactsURL, bytes.NewReader(payload))
+		req, err := http.NewRequest("POST", pc.endpointURL, bytes.NewReader(payload))
 		if err != nil {
 			finalErr = fmt.Errorf("failed to create new contact request: %w", err)
 			continue
diff --git a/test/pardot-test-srv/main.go b/test/pardot-test-srv/main.go
index e247ff345..a40879d42 100644
--- a/test/pardot-test-srv/main.go
+++ b/test/pardot-test-srv/main.go
@@ -85,7 +85,7 @@ func (ts *testServer) checkToken(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-func (ts *testServer) createContactsHandler(w http.ResponseWriter, r *http.Request) {
+func (ts *testServer) upsertContactsHandler(w http.ResponseWriter, r *http.Request) {
 	ts.checkToken(w, r)
 
 	businessUnitId := r.Header.Get("Pardot-Business-Unit-Id")
@@ -100,19 +100,22 @@ func (ts *testServer) createContactsHandler(w http.ResponseWriter, r *http.Reque
 		return
 	}
 
-	type contactData struct {
-		Email string `json:"email"`
+	type upsertPayload struct {
+		MatchEmail string `json:"matchEmail"`
+		Prospect   struct {
+			Email string `json:"email"`
+		} `json:"prospect"`
 	}
 
-	var contact contactData
-	err = json.Unmarshal(body, &contact)
+	var payload upsertPayload
+	err = json.Unmarshal(body, &payload)
 	if err != nil {
 		http.Error(w, "Failed to parse request body", http.StatusBadRequest)
 		return
 	}
 
-	if contact.Email == "" {
-		http.Error(w, "Missing 'email' field in request body", http.StatusBadRequest)
+	if payload.MatchEmail == "" || payload.Prospect.Email == "" {
+		http.Error(w, "Missing 'matchEmail' or 'prospect.email' in request body", http.StatusBadRequest)
 		return
 	}
 
@@ -122,7 +125,7 @@ func (ts *testServer) createContactsHandler(w http.ResponseWriter, r *http.Reque
 		// with a small number of contacts, so it's fine.
 		ts.contacts.created = ts.contacts.created[1:]
 	}
-	ts.contacts.created = append(ts.contacts.created, contact.Email)
+	ts.contacts.created = append(ts.contacts.created, payload.Prospect.Email)
 	ts.contacts.Unlock()
 
 	w.Header().Set("Content-Type", "application/json")
@@ -198,7 +201,7 @@ func main() {
 
 	// Pardot API Server
 	pardotMux := http.NewServeMux()
-	pardotMux.HandleFunc("/api/v5/objects/prospects", ts.createContactsHandler)
+	pardotMux.HandleFunc("/api/v5/objects/prospects/do/upsertLatestByEmail", ts.upsertContactsHandler)
 	pardotMux.HandleFunc("/contacts", ts.queryContactsHandler)
 
 	pardotServer := &http.Server{