# X_MAIL_DRIVER_UNAVAILABLE

## Means

no mail driver is configured

## Typical cause

no `mail:` in `apps/<app>/runtime.ts` and no transport variable set

## Fix

`export const runtime = { mail: memoryMailDriver() }` in `apps/<app>/runtime.ts` for dev, or set `SMTP_URL` (or `RESEND_API_KEY`) in `.env` so the boot selects a live driver

[Mail](/error-codes#mail)