Before addinganother plugin.
An SMTP plugin often does not fix it, because the cause is not the plugin — it is the domain's mail configuration. Work through it in order, then add only what is actually needed.
Steps
Check the domain
Gmail and Yahoo refuse mail from domains without authentication. Shared hosting's default sending usually lacks it. No account needed to find out.
https://nintact.com/en/check?domain=example.comFix the From address
Putting the submitter's address in From — the widely copied pattern — means claiming someone else's domain, and it cannot pass authentication. Send as your own address and put theirs in Reply-To. This alone fixes the most cases.
Repoint the action
Keep the form. Changing where it posts leaves the markup, fields and styling untouched, and mail then leaves over an authenticated domain with nothing published on your DNS.
<form action="https://nintact.com/api/f/YOUR_FORM_ID" method="POST">
<!-- your existing inputs stay exactly as they are -->
</form>Or paste one line for a new form
A custom HTML block is enough. No plugin to install, no server settings to change.
<script src="https://nintact.com/embed.js"
data-nintact="YOUR_FORM_ID" async></script>Questions
Can I keep Contact Form 7?
Yes. Repointing the action leaves the form you built exactly as it is.
Will an SMTP plugin fix it?
It fixes the route out, which is sometimes not enough: unless you also verify your domain with that provider by publishing DNS records, the receiver still sees unauthenticated mail.
Do I have to move hosting?
No. The site and the server stay where they are; only the form's receiving and notification move.
Where do inquiries end up?
Stored in the dashboard, sorted, with a reply drafted. If a notification lands in spam, the content is still there.