M365 Messaging Architect: Exchange & Tenant Migrations

Jobtailor; Greater London; On-site; GBP 90,000 - 125,000; Full time

Job summary

Jobtailor is seeking an experienced Messaging Architect to own the end-to-end messaging architecture during a Microsoft 365 transformation. You will lead technical delivery across Exchange Online, hybrid and multi-tenant environments, defining migration patterns, mail routing, DNS, security controls and governance alignment.

The role requires strong architectural judgement, stakeholder management and the ability to resolve complex cross-boundary issues while ensuring continuity during cutover

Qualifications

• Extensive architecture experience across Exchange Online, Microsoft 365 and enterprise messaging environments.
• Proven experience designing hybrid and/or multi-tenant messaging architectures.
• Strong experience delivering tenant-to-tenant mailbox migrations and complex coexistence arrangements.

Responsibilities

• Own the messaging architecture and provide technical leadership across the transformation lifecycle.
• Assess the current Exchange and Microsoft 365 estate, including tenants, domains, mail flow, recipients, dependencies, integrations and operational arrangements.
• Identify architectural constraints, technical debt, risks and dependencies.
• Define coexistence and target-state messaging architectures across Microsoft 365 tenants, existing Exchange environments and retained services.
• Establish architectural principles and standards for messaging migration and modernisation.
• Design secure and resilient mail-routing architectures.
• Define accepted-domain, DNS, MX, Autodiscover and service-discovery arrangements.
• Define address-list, Global Address List and recipient-visibility strategies.
• Design calendar interoperability, free/busy and scheduling arrangements.
• Develop migration patterns for user, shared, resource and service mailboxes, distribution groups, contacts and other messaging objects.
• Establish migration sequencing covering discovery, readiness assessment, pilots, production waves, testing, cutover and post-migration support.
• Define technical entry and exit criteria for migration waves.
• Assure mail-flow continuity, including internal, external and cross-environment routing.
• Define controls for transport rules, connectors, email security and delegated access.
• Align messaging architecture with retention, compliance, eDiscovery, journalling and information-governance requirements.
• Work with security specialists to define controls using Microsoft Defender for Office 365.
• Assess dependencies involving identity synchronisation, applications, SMTP relay, collaboration services, mobile access and endpoint technologies.
• Resolve application email dependencies and define secure SMTP relay and application-to-mail integration patterns.
• Coordinate with identity, collaboration, application, network, security, EUC, service-transition and change teams.
• Review technical designs and migration approaches, providing architectural assurance.
• Support detailed migration and implementation plans while retaining ownership of the messaging architecture.
• Define rollback, recovery and contingency approaches.
• Support cutover decisions and provide technical assurance during major migration events.
• Provide guidance during early-life support and help resolve complex cross-boundary issues.
• Produce and maintain HLDs, LLDs, architecture diagrams, migration patterns, technical standards, decision records and design documentation.
• Document and communicate architectural decisions, assumptions, dependencies and risks

Skills

Exchange Online Architecture

Microsoft 365 Messaging Design

Tenant-to-Tenant Migrations

Email Security with Defender

Architecture Documentation

Tools

Microsoft 365

Exchange

Defender for Office 365

Third-Party Migration Tooling

Job description

Jobtailor is seeking an experienced Messaging Architect to own the end-to-end messaging architecture during a Microsoft 365 transformation. You will lead technical delivery across Exchange Online, hybrid and multi-tenant environments, defining migration patterns, mail routing, DNS, security controls and governance alignment.

The role requires strong architectural judgement, stakeholder management and the ability to resolve complex cross-boundary issues while ensuring continuity during cutover