The gateway is the road your message travels. Mersal gives you more than one road per channel, and each has different costs, reliability and limits. Choosing wrong here costs you money or banned numbers.
WhatsApp gateways
1) WhatsApp QR (device linking)
You link a normal WhatsApp number by scanning a QR code, exactly like WhatsApp Web. Upsides: zero per-message cost, live in minutes, and the number your customers already know stays the same.
Downsides: it's subject to normal WhatsApp policy, so it can be banned if misused. Best for small and mid-sized businesses and two-way conversations.
2) WhatsApp Cloud API (from Meta)
The official route: an approved WABA account with embedded signup. Upsides: far higher reliability, a verified badge, and approved template messages. Downsides: a per-conversation cost, and templates need approval before use. Best for larger businesses and critical operational alerts.
SMS gateways
1) An external SMS provider
Twilio, Vonage, or any provider that speaks HTTP. Gives you a custom sender ID and real delivery reports (DLR). Best for bulk sending and verification codes.
2) Android SIM
Turns an Android phone with your own SIM into an SMS gateway through the Mersal app. Your cost becomes your normal SIM bundle instead of international per-message pricing — a huge difference for small businesses. Downsides: throughput is limited by the SIM, and it needs a phone kept on power and internet.
The email gateway
SMTP configuration for your provider with a built-in send test. It's essential to add a sending domain and enable DKIM (covered in detail in a separate article) or your mail will be classified as spam.
Cost and limits — the practical differences
The exact numbers vary by provider and country, but the cost ordering is effectively constant:
- WhatsApp QR: zero per message. Your only cost is the device's data plan. Practical throughput is tens of messages per minute per number.
- Cloud API: billed per 24-hour conversation rather than per message, so once a customer replies and you're in a thread the cost stays singular. Throughput is far higher with no practical ceiling at mid volumes.
- SMS provider: the most expensive per message, and it varies widely between networks and countries. But it's the only channel that reaches any handset with no internet at all.
- Android SIM: whatever a local message costs in your bundle. Throughput is the bottleneck — local SIMs usually hit a daily cap.
- Email: cheapest by a wide margin per thousand recipients, but inbox placement depends on your domain reputation rather than your provider.
Quick selection guide
- Want to start today at minimum cost? WhatsApp QR + Android SIM.
- Sending operational alerts that cannot fail? Cloud API + an SMS provider.
- Sending newsletters and catalogues? SMTP on an authenticated domain.
- Sending verification codes? WhatsApp first with SMS as fallback — cheaper and faster, with SMS covering anyone not on WhatsApp.
Setting each gateway up
- WhatsApp QR: from the Mersal dashboard, add a device and scan the code from WhatsApp on your phone. Keep the phone online. If the session drops, rescan from the same screen.
- Cloud API: you need a Facebook page and a business account. You go through embedded signup inside Mersal, then add and verify a number, and submit your templates for approval before the first campaign.
- SMS provider: take an API key from the provider into Mersal, and register your sender ID with the provider — registration takes time in some countries, so start it early.
- Android SIM: install the Mersal app on an Android phone, sign in, grant SMS permission. Keep the phone on a charger and exclude the app from battery optimisation or the OS will suspend it.
- SMTP: provider credentials, a sending domain, SPF and DKIM records in DNS, then a send test from inside Mersal.
You don't have to pick just one
The best practical setup is a mix: Cloud API for critical alerts, QR for daily conversations, Android SIM for cheap SMS. Mersal lets you define several gateways for the same channel and choose the gateway per campaign.
More useful still: you can nominate a fallback gateway. If a WhatsApp message isn't delivered within the window you set, it re-sends over SMS automatically. That raises real reach without paying two channels' cost for every customer.
Common gateway mistakes
- Using QR for critical alerts: an order notification that fails to arrive is an operational problem. Critical traffic deserves Cloud API.
- Linking the same WhatsApp number to more than one tool: it drops the session constantly and raises ban risk.
- Leaning on an Android SIM for a huge campaign: the SIM hits its daily cap and the campaign stalls halfway.
- Sending email from a domain with no DKIM: inbox placement falls below half whatever the provider.
- Not registering a sender ID: in many countries messages from an unregistered sender are blocked outright.
Frequently asked questions
Can I use more than one WhatsApp number? Yes, and it's the better setup at volume — Mersal spreads the load across them automatically.
Can I change gateway without rebuilding my campaigns? Yes, the gateway is configured separately from the campaign, so you can switch without touching anything else.
What happens if a provider goes down? If you have more than one gateway defined for that channel, sending continues on the other one.
