Does it make sense to a user that this field is for email only? Or is it confusing?
It does need a label, not just visually for people viewing the site but for people using assistive technologies (screenreaders etc). If there is no label then people visiting do not know what the field is for, or what goes it it.
3.3.2 Labels or Instructions: Labels or instructions are provided when content requires user input. (Level A)
Having no label means you don't even conform to the bare minimum accessibility standard.
I would say give it a label.
Also, as a side note, "go" doesn't seem like the right CTA on the button. "Submit", "enroll" or "sign-up" would all be better options. "Go" implies you'll be moving the user to another page for next steps, while language that indicates this is a submission field would make more sense. If you actually are taking them to a page where you get more details, then don't ask for any information now, get them to the full form as simply as possible.
Replace the button text
Join or Join our mailing list.
Because that is what the button is doing.
Put an example email like firstname.lastname@example.org on the textbox (or input), if thats a webapp you can safely use the
Don't worry, !! we respect your privacy we never spam.
We never spam.
Remember that you should provide an email validation.
If you still want to show the Email label, check how mailchimp solved this problem
I'd have to imagine there would be some text somewhere around this field that would explain a little about your mailing list (e.g. how often to expect emails, what kind of content to expect, etc.). If not, you should really consider adding this. I struggle to imagine many visitors clamoring to enter something into a random field with very little context.
Once you have some copy about the mailing list within the context of that sign up field, the field itself becomes much less ambiguous and the significance of the label becomes much less critical.
I do agree with the general sentiment that a label is required, and the CTA should be clearer. With some copy to help provide context to the field, I can see something like this:
--------------------- ---------- | your email | | JOIN | --------------------- ----------