Nginx session-stickiness

[Buzzz]

Hi

I'm trying to configure an smtp proxy.
I've wrote my own perl auth handler and my backend smtp server does not
use smtp-auth.

I've seen that nginx smtp proxy try to smtp-auth with the backend after a
successful auth from the smtp client.

Is it possibile to disable this ? i would like that nginx talk with the
smtp backend without auth , just forward the smtp-client data (mail) to
the smtp backend.

Thx for help,
Davide