diff --git a/src/Customer.php b/src/Customer.php
index 064d21d..bafe77d 100644
--- a/src/Customer.php
+++ b/src/Customer.php
@@ -91,7 +91,8 @@ class Customer extends BaseCustomer {
 	public function mailboxesThroughConversations() {
 		return $this
 			->conversations
-			->pluck('mailbox');
+			->pluck('mailbox')
+			->unique();
 	}
 
 	/**