Error codes

sender_not_verified

The "from" domain isn't verified on your workspace.

Status: 422 · Code: sender_not_verified

You can only send from domains that are added and verified on your workspace. This protects deliverability — and is required by every mail provider.

Common causes

The domain isn't added yet — only send0.dev or your *.yourdomain.com test sandbox works
The domain is added but DKIM / SPF / DMARC verification hasn't passed
You're sending from a public provider (@gmail.com, @outlook.com) — we'll never allow that

How to fix

Go to app.send0.dev/domains and add your domain if it isn't there.
Add the DNS records we show you — specifically DKIM (two CNAMEs) and SPF (one TXT).
Click Verify. Most DNS propagates in under 5 minutes; some registrars take longer.
Once status shows verified, send again.

Until verification lands, use sandbox@send0.dev as the from — it works with any sk_test_ key.

Sending domains · Deliverability 101

validation_error

One or more fields on your request failed validation.

too_many_recipients

You tried to send to more than 50 addresses on a single send.

On this page

Common causes How to fix Related