DreamHost has a fairly simple anti-spam policy, which can be summed up as this: You cannot send email from an address that isn’t your domain.
If that was greek to you, don’t worry. What that means is that my WordPress blog here can only send emails as elftest.net. That poses a small problem if you’re not using your domain-name to send email (a rare occurrence in WordPress), and a large one if you happen to be using the popular Contact Form 7 plugin.
Contact Form 7 lets you create robust contact forms for your site, however it has one minor ‘flaw’ (and I hesitate to use that word). When it sends email, it sends it from the user who submits the form. DreamHost, naturally, doesn’t like this. firstname.lastname@example.org isn’t an elftest user!
Thankfully there’s a work-around for you, and it’s really easy. For most people, the plugin SMTP Configure, once installed and activated, will automatically fix this for you! It’s written by a reliable and trusted programmer, and I highly recommend it. Remember! Once you install the plugin, just activate it. For the vast majority of people, this was it. Everything magically worked.
Then there were some people who came and said “No, this does not work.” I’ve yet to reproduce it, but one person told me that after putting in his SMTP credentials, just like you would setting up email clients, it worked perfectly.
Additional: If you’re using Jetpack’s contact form, and you’ve changed the ‘to’ email address, you will also need this plugin. You’ll know you’re using that option because you’ll see this in your contact form shortcode: