How to add DKIM when smtp sending via gmail using phpmailer?

Question

gmail

I send emails via phpmailer in smtp mode. Letters reach, but they do not have DKIM.
If you send via gmail's web-interface - DKIM - yes. Yes, DKIM for google apps is configured.
If you add dkim to phpmailer - it turns out not valid. But, only when sending smtp, via gmail. In the normal mode of sending DKIM, it turns out to be valid.
those. either gmail but without dkim, or with dkim but without gmail.
And I would like both gmail and dkim. Any ideas?