Mariusz O.

I'm an Email Developer and Email Marketing Strategist with a programming background in AI-powered automation and system architecture. With 15+ years of experience, 4,000+ projects delivered for 1,900+ clients worldwide, I build production-ready email systems - not just templates - combining clean HTML/CSS, lifecycle automation, marketing strategy, deliverability expertise, and AI-driven workflows under one roof. Top Rated Plus on Upwork with $700K+ in earnings. What I do: 1. Email Development (Core) Custom HTML/CSS email builds - mobile-responsive, dark-mode-ready, cross-client tested. I work across Mailchimp, HubSpot, Salesforce / Pardot, Marketo, Klaviyo, ActiveCampaign, Campaign Monitor, SendGrid, and Iterable. In 2015, Mailchimp recognised me for identifying and fixing critical rendering bugs in their templates. Certified Mailchimp Partner. 2. Email Marketing Strategy & Execution End-to-end email marketing - audits, campaign planning, segmentation, lifecycle automation (welcome, nurture, re-engagement, winback), A/B testing, and performance optimisation. I build scalable, compliant email programs with predictable long-term performance. I handle both strategy and execution end-to-end. 3. AI Architecture & Intelligent Automation I build AI-powered audit and automation systems connected directly to your ESP/CRM via MCP servers. AI analyses your flows, campaigns, deliverability, and engagement data in real time - producing structured audit reports and prioritised fix lists. Examples: automated Klaviyo flow audits with copy rewrites, real-time deliverability monitoring, and engagement scoring. I also build RAG MCP servers that let AI reference your internal docs, brand guidelines, and performance history during audits and content generation. 4. Front-End & Automation Development Custom applications, internal tools, dashboards, and integrations using JavaScript, Python, React, Google Apps Script, and n8n. I connect CRMs, ESPs, databases, Google Sheets, and APIs into unified automated workflows. Core services: ★ Custom email development (HTML/CSS, dark mode, responsive, cross-client) ★ Email marketing strategy, audits & campaign execution ★ AI-powered ESP/CRM audits via MCP server integration ★ RAG MCP servers for context-aware AI recommendations & content generation ★ Lifecycle automation (welcome, onboarding, nurture, re-engagement, winback, lead scoring) ★ Deliverability setup & troubleshooting (SPF, DKIM, DMARC, sender reputation) ★ Segmentation strategy (openers, clickers, inactive users, RFM, predictive) ★ A/B testing, reporting & performance optimisation ★ Advanced ESP customisation (HubSpot HubL, Salesforce AMPscript, Marketo Velocity) ★ AI agents & n8n automation systems ★ CRM & ESP integrations (HubSpot, Salesforce, Marketo, Mailchimp, Klaviyo, ActiveCampaign) ★ Custom Google Sheets & Apps Script solutions (dashboards, triggers, integrations) ★ API-based integrations & webhook workflows ★ Cross-client email testing (Litmus, Email on Acid, dark mode, Outlook VML fixes) Why work with me: ★ 15+ years in email development and email marketing ★ 4,000+ projects for 1,800+ clients (Microsoft, Netflix, Unilever, Toyota, Adobe, BBC, Meta, Amazon Prime Video, TikTok, Adidas, Sony, Coca-Cola, Hyundai, LG, Renault, Bayer, 3M, and more) ★ Member of 32 Upwork Talent Cloud groups (Enterprise Professionals, Microsoft UTC, Netflix Print Production, Unilever, Tata Communications, Holland & Barrett, Janus Henderson, and others) ★ AI-powered audit and automation capabilities (MCP + RAG architecture) ★ End-to-end ownership - strategy, development, execution, optimisation ★ Clean, maintainable code and scalable architecture Certificates: HubSpot Marketing Software, HubSpot Email Marketing, HubSpot Contextual Marketing, Mailchimp Email Automations, Mailchimp Foundations, Python (Alison), Salesforce for Admins, Managing DNS, Advanced CSS Media Queries, Google Ads Measurement. Skills: HTML5, CSS, Email Development, Email Deliverability, AMPscript, HubSpot HubL, Marketo Velocity, JavaScript, Python, React, Google Apps Script, n8n, APIs & Webhooks, MCP Servers, RAG Architecture, AI Agents, Marketing Automation, CRM Integrations I use AI as a development and analysis accelerator - speeding up coding, testing, auditing, and iteration - while maintaining full control over architecture, logic, and production quality. Availability: ★ Mon–Thu: 3:00 AM – 11:00 AM EST, 3:00 PM – 7:00 PM EST ★ Friday: 3:00 AM – 11:00 AM EST