Inbox OSS is API-compatible with SendGrid v3. The minimum-viable migration is two changes:
1. Hostname. api.sendgrid.com → api.inbox.onesourcesoft.com.
2. API key. SG.xxx → your Inbox OSS key.
That's it for code. SDKs work as-is. Templates render the same. Webhook payloads are identical.
Optional but recommended: - Import your SendGrid suppression list via /v3/suppressions/bulk (CSV format identical). - Update DNS to add Inbox OSS sending domain CNAMEs (can run alongside SendGrid for parallel testing). - Run 1% traffic through Inbox OSS for 48 hours before full cutover.
Full guide at /solutions/migrate-sendgrid.