Multi-Tenant Invoicing & Accounting SaaS with White-Label & Custom SMTP
Built a full multi-workspace invoicing and accounting platform with unlimited customers/invoices, custom SMTP, white-label domains, income/expense tracking, and real-time P&L reporting — trusted by 500+ freelancers and agencies.
Legacy Bottlenecks & Technical Constraints
Freelancers and small agencies were stuck between free limited tools and expensive accounting software. They needed unlimited invoices, multi-business workspaces, professional branded email delivery, and built-in financial reporting without monthly per-user fees.
Architectural Design & Implementation
Soft Clerk engineered a complete multi-tenant SaaS on Next.js + Prisma + PostgreSQL with row-level isolation, custom SMTP configuration, white-label domain support, and real-time financial dashboards.
Engineered Technical Architecture
How data and execution flows through the system from edge ingestion to persistent storage.
Workspace & Tenant Isolation
User creates or switches workspaces. Prisma middleware injects tenant_id on every query, guaranteeing complete data isolation.
Invoice Generation & PDF
Client data + line items are rendered into professional templates and converted to PDF on the edge with sub-second latency.
Custom SMTP Dispatch
User-configured SMTP credentials are encrypted and used to send invoices from the client’s own domain for maximum deliverability.
Financial Aggregation
Income, expenses, and invoice status feed into real-time dashboards and exportable P&L statements.
Key Engineering Obstacles & Solutions
Real technical challenges encountered during implementation and how our engineering team overcame them.
Secure Multi-Workspace Data Isolation
A single compromised session or incorrect query could leak data across organizations.
Implemented Prisma client extensions that automatically inject and enforce tenant_id filters on every model, combined with JWT claims containing active workspace context.
Reliable Custom SMTP Across Providers
Users bring Gmail, Outlook, SendGrid, SES, or raw SMTP credentials with widely varying auth requirements.
Built a provider-agnostic SMTP abstraction layer with connection testing, credential encryption at rest, and graceful fallback messaging when delivery fails.
Delivery Phases & Milestones
Structured milestone delivery ensuring total transparency and zero project drift.
Core Schema & Multi-Tenancy
- PostgreSQL schema with workspace isolation model
- Next.js App Router + Prisma + Auth.js foundation
- Basic invoice CRUD and PDF generation
Collaboration, SMTP & White-Label
- Team invites + role-based access control
- Custom SMTP configuration UI and encrypted storage
- White-label branding and custom domain support
Accounting Features & Launch
- Income/expense tracking and P&L reports
- Stripe billing + lifetime deal logic
- Production deployment, monitoring, and documentation handover
Core Technologies Deployed
Production technologies selected for high performance, zero technical debt, and enterprise scale.
Quantifiable Business & Engineering Outcomes
Professional invoices generated and sent by freelancers and agencies worldwide.
Paying and free users actively managing customers and finances on the platform.
Users report significant reduction in weekly administrative overhead.
“Classified Billing transformed our agency workflow completely. We’re now processing 300% more invoices with half the effort. The multi-workspace feature is pure genius.”
Production Assets Handed Over
Full intellectual property transfer with zero proprietary vendor lock-in.
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