[Mailer] Fix an error message

Author: fabpot

Tests/Transport/DsnTest.php

@@ -77,12 +77,12 @@ public function invalidDsnProvider(): iterable
 
         yield [
             '//sendmail',
-            'The "//sendmail" mailer DSN must contain a transport scheme.',
+            'The "//sendmail" mailer DSN must contain a scheme.',
         ];
 
         yield [
             'file:///some/path',
-            'The "file:///some/path" mailer DSN must contain a mailer name.',
+            'The "file:///some/path" mailer DSN must contain a host (use "default" by default).',
         ];
     }
 }

Transport/Dsn.php

@@ -42,11 +42,11 @@ public static function fromString(string $dsn): self
         }
 
         if (!isset($parsedDsn['scheme'])) {
-            throw new InvalidArgumentException(sprintf('The "%s" mailer DSN must contain a transport scheme.', $dsn));
+            throw new InvalidArgumentException(sprintf('The "%s" mailer DSN must contain a scheme.', $dsn));
         }
 
         if (!isset($parsedDsn['host'])) {
-            throw new InvalidArgumentException(sprintf('The "%s" mailer DSN must contain a mailer name.', $dsn));
+            throw new InvalidArgumentException(sprintf('The "%s" mailer DSN must contain a host (use "default" by default).', $dsn));
         }
 
         $user = isset($parsedDsn['user']) ? urldecode($parsedDsn['user']) : null;