Custom domain
Your install runs on email.your-agency.com, not acelle.someone.io. Customers log in there, build campaigns there, see reports there. The email sender domain (DKIM / SPF / DMARC) is a separate setting per Customer — each end client's transactional mail goes out from their verified domain, not yours.
Branded admin UI
The admin Settings page covers logo, primary colour, login-page layout, and footer copy. Themes are first-class Laravel views in resources/views/refactor/; agencies that need full UI customisation can fork the theme into a plugin and ship a per-client variant — see UI injection.
Per-client plans
Free / Starter / Pro tiers; quota enforcement on contacts, campaigns, and monthly sends; daily caps; allowed feature subsets. Plan upgrades and downgrades flow through the bundled Cashier package or a payment-gateway plugin for regional vendors (Paddle, Razorpay, Paystack, Mollie, etc.).
Multiple sending servers
One sending server per client (or shared pool, your call). Amazon SES with separate IAM identities, SendGrid sub-accounts, custom Postal MTA — each client's campaigns route through the server you assigned, with per-server reputation isolated. New vendors ship as a one-class sending-driver plugin.
Customer self-service
End clients log in to the customer side of the admin and build their own campaigns, lists, automations, A/B tests. The agency admin watches the meta-view: per-client sending volume, plan utilisation, billing status, deliverability metrics. Two completely separate UIs sharing the same database — no hand-built portal required.
Reseller-grade observability
Per-client sending volume, bounce rate, complaint rate, open rate trends, top-domain failures. The admin observability page rolls up across every customer; per-customer drill-down shows the same data scoped to one tenant. Cron-driven daily rollup means the page renders cheaply even with hundreds of clients.