diff --git a/email/worker.go b/email/worker.go
index e2f48964697e3e04e61eb1b81775579550a07c48..fb9cb89cdc46b2a709f89685cbc32126b34167aa 100644
--- a/email/worker.go
+++ b/email/worker.go
@@ -72,6 +72,14 @@ 		return nil, errors.New("Expected user PGP key to contain one key")
 	}
 	rcptEntity := keyring[0]
 
+	// Make sure we can really encrypt with this key!
+	// pgpmail.Encrypt() returns a writer, and certain errors will only
+	// occur once it is written to.
+	_, ok := rcptEntity.EncryptionKey(time.Now())
+	if !ok {
+		return nil, fmt.Errorf("No valid encryption key found (expired?)")
+	}
+
 	return pgpmail.Encrypt(buf, header.Header.Header,
 		[]*openpgp.Entity{rcptEntity}, signed, nil)
 }