Using an e-mail service provider
If you want to send authenticated e-mail but don't want to set it up on your own, almost all reputable e-mail service providers (ESPs) already support authentication. Any of them should be able to either publish your authentication records for you or give you guidance on how to publish them. If all of your e-mail goes through the ESP, then you're done! If you maintain corporate e-mail servers separate from those of your ESP, though, you'll still need to set up authentication for your own domain(s).
Using an ISP account
If you use an e-mail address from your ISP, your e-mail address will look similar to [email protected], for example, and you won't have any access to the DNS for your e-mail domain.
The good news is that many of the major ISPs are authenticating their outgoing mail. The bad news is that, because you are sharing the authentication identity with all the other customers of your ISP, the authentication won't do you much good. There are likely many "legitimate" customers of your ISP who are using their accounts to send out abusive e-mail.
If you want to be able to build up a positive sender reputation that really belongs to you, your own authentication domain-either managed on your own or by using an ESP or ISP-is really your only viable option.