Sender IDs

The sender ID is what recipients see as the message sender. You pass it as sender_id in every send request.

Rules

Rule	Detail
Length	3–11 characters
Charset	Alphanumeric (A–Z, a–z, 0–9)
First character	Must not be a digit
Examples	MyCompany, PromoAlert, AcmeStore

Invalid sender IDs are rejected with 400 INVALID_SENDER.

Alphanumeric vs numeric senders

• Alphanumeric (MyApp) — best for branding; recipients cannot reply.
• Phone number (+14155551234) — allows replies where supported; also accepted as sender_id.

Country restrictions

Sender ID handling differs by destination country: some carriers pass alphanumeric senders as-is, others overwrite them with a generic ID or a short code, and some require pre-registration of sender names.

Tip

If a specific sender name is critical for your campaign in a particular country, ask your account manager about registration requirements for that destination before going live.

Best practices

• Stay consistent — one recognizable sender per use case builds trust and improves engagement.
• Match your brand — Acme beats ACM3X9. Avoid anything that looks like spam or a random string; carriers filter aggressively.
• Don’t rotate senders to dodge filters — it hurts deliverability and can get traffic blocked entirely.
• Test per country — send to a local number and verify what the handset actually displays before launching.