actually I don't use DKIM and DOMAIN KEY, but only SPF.
I want to utilize all three but I have somehow doubt.
I have SmarterMail Enterprise for incoming e-mail.
For outgoing e-mail to internet, e-mail is delivered by same SmarterMail server if e-mail is send from webmail or e-mail client.
If e-mail is send from my customer website, I use another server, with SmarterMail free, for delivery to internet, and I not pass from SmarterMail server.
If I implement DKIM and DOMAIN KEY, only e-mail passed from main SmarterMail server use this.
I would not use the main SmarterMail server also for emails to be sent from websites to the Internet, because I think to overload it, but if there is no other way I will be forced.
As you advise me to do?