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
API length	3–11 characters
API charset	ASCII alphanumeric characters (A–Z, a–z, 0–9)
API first-character rule	Must not start with a digit
API blank handling	Missing, blank or invalid values return 400 INVALID_SENDER
Examples	MyCompany, PromoAlert, AcmeStore

Country and route support is still account-dependent; some destinations may require sender registration before traffic goes live.

Alphanumeric vs numeric senders

• Alphanumeric (MyApp) — best for branding; recipients cannot reply.
• Numeric sender — not accepted by the public API send endpoints; use an approved alphanumeric sender or ask support about route-specific options.

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.