M365 Architect - Exchange/Messaging

Salary: £70,000 - 110,000 per year

• 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.
• Expert knowledge of mail routing, connectors, accepted domains, transport rules and recipient management.
• Strong understanding of DNS, MX records, Autodiscover and messaging-related service discovery.
• Experience designing address-list, calendar, free/busy and collaboration arrangements across multiple environments.
• Proven experience defining migration strategies for user, shared, resource and service mailboxes.
• Strong knowledge of email security, including Microsoft Defender for Office 365.
• Good understanding of retention, eDiscovery, journalling, compliance and information-governance requirements.
• Strong understanding of identity synchronisation and the relationship between identity architecture and messaging.
• Experience designing and troubleshooting SMTP relay and application-to-email integrations.
• Experience working with Microsoft and third-party messaging migration tooling.
• Strong understanding of client and end-user considerations, including Outlook, mobile access and user experience during migration.
• Experience designing migration sequencing, pilot approaches, testing, cutover and rollback strategies.
• Strong architecture documentation skills, including HLDs, LLDs, diagrams, technical standards and architecture decision records.
• Strong troubleshooting and analytical skills across messaging, DNS, identity, applications and client technologies.
• Experience working with third-party suppliers and technical delivery partners.
• Strong stakeholder-management and influencing skills, with the ability to communicate complex technical decisions clearly.

• Assess the current Exchange and Microsoft 365 estate, including configuration, tenants, domains, mail flow, recipients, dependencies, integrations and existing operational arrangements.
• Identify architectural constraints, technical debt, risks and dependencies that could affect the transformation.
• Define coexistence and target-state messaging architectures across relevant 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 across existing and target environments.
• Define accepted-domain strategies and address dependencies associated with domain ownership, DNS and mail routing.
• Design DNS, MX, Autodiscover and service-discovery arrangements required to support coexistence and migration.
• Define address-list, Global Address List and recipient-visibility strategies appropriate to the target environment.
• Design calendar interoperability, free/busy and scheduling arrangements during the transition.
• Develop migration patterns for user, shared, resource and service mailboxes, as well as distribution groups, contacts and other messaging objects.
• Define appropriate approaches for different mailbox and messaging-object types, recognising that not all services will have the same migration requirements.
• Establish migration sequencing, including discovery, readiness assessment, pilots, production waves, testing, cutover and post-migration support.
• Define technical entry and exit criteria for messaging migration waves.
• Design and assure mail-flow continuity throughout migration, including internal, external and cross-environment routing.
• Define controls for transport rules, connectors, email security and delegated access.
• Ensure messaging architecture aligns with organisational requirements for retention, compliance, eDiscovery, journalling and information governance.
• Work with security specialists to define appropriate controls using capabilities such as Microsoft Defender for Office 365.
• Assess dependencies between messaging and identity synchronisation, applications, SMTP relay, collaboration services, mobile access and endpoint technologies.
• Work with application teams to understand and resolve dependencies where applications send or receive email.
• Define patterns for SMTP relay and application-to-mail integrations, ensuring they are secure, supportable and aligned with the target architecture.
• Coordinate with identity, collaboration, application, network, security, EUC, service-transition and change teams to ensure messaging dependencies are properly managed.
• Review technical designs and migration approaches produced by engineering and delivery teams, providing architectural assurance.
• Support the development of detailed migration and implementation plans while retaining ownership of the overall messaging architecture.
• Define rollback and recovery approaches for messaging migrations and ensure appropriate contingency arrangements are considered.
• Support cutover decision-making and provide technical assurance during major migration events.
• Provide architectural guidance during early-life support and help resolve complex issues that cross messaging, identity, DNS, application or client boundaries.
• Produce and maintain HLDs, LLDs, architecture diagrams, migration patterns, technical standards, decision records and design documentation.
• Ensure that architectural decisions, assumptions, dependencies and risks are clearly documented and communicated.

• Architect
• Flow
• Support
• Microsoft 365
• Mobile
• Network
• Office 365
• Security

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We are Methods Business and Digital Technology Limited, a UK-based IT services consultancy established over 30 years ago and part of the Alten Group since early 2022. We work with central government departments and agencies, and we are also building a significant private sector client portfolio. We are looking for an experienced Exchange / Microsoft 365 / Messaging Architect to join a major technology transformation programme in a key architecture role. The position is initially onsite in London and then offers a 50/50 hybrid working arrangement. We offer a supportive and collaborative environment, opportunities for development and training, flexible working, 25 days of annual leave plus bank holidays with the option to buy 5 extra days, paid volunteering days, pension, life assurance, private medical insurance, worldwide travel insurance, enhanced maternity and paternity pay, and travel benefits including a season ticket loan and cycle to work scheme.

last updated 36 week of 2026