Microsoft 365 for Accounting Firms: What Actually Matters

Choosing the right license tier

Microsoft 365 Business Premium includes Defender for Office 365 email protection, conditional access, and device management features that Business Standard does not, and these are not optional extras for a firm handling client financial data. The price difference per user is small compared to the cost of a single successful phishing attack against a firm holding banking and tax information for dozens of clients.

Email security priorities for accounting firms

• Multi-factor authentication enforced on every account without exception, including partners and senior staff
• Defender for Office 365 anti-phishing policies tuned for the invoice and payment fraud attempts accounting firms are frequently targeted with
• Safe Attachments and Safe Links enabled to catch malicious documents disguised as client files
• External email tagging so staff can immediately spot messages impersonating clients or vendors

Conditional access and device management

Conditional access policies can require that email and document access only happen from managed, compliant devices, or add extra verification steps for sign-ins from unusual locations. This matters particularly during tax season when temporary staff or contractors may need limited access, a scenario also covered in our tax season IT readiness guide.

Retention and data governance

1. Set mailbox retention policies that align with how long the firm needs to retain client correspondence for its own records
2. Apply data loss prevention rules to flag emails containing patterns like SIN numbers or banking details being sent externally
3. Use SharePoint and OneDrive access controls to limit which staff can see specific client folders, rather than granting broad access by default
4. Review and remove access for departed staff and expired contractor accounts promptly

How Microsoft 365 fits with document exchange

Many firms already use Microsoft 365's SharePoint or OneDrive as the backbone for exchanging documents securely with clients, which overlaps directly with the practices covered in our secure client document exchange guide. Configuring external sharing links with expiration dates and access restrictions, rather than open links, is one of the simpler improvements most firms can make quickly.

Backup: what Microsoft 365 does and does not cover

Microsoft's own retention and recycle bin features are not a substitute for a dedicated backup of Microsoft 365 data. Accidentally deleted mailboxes, malicious deletion, or retention policy expiry can all result in permanent data loss without a separate backup in place, which is why we pair Microsoft 365 deployments with our backup and disaster recovery services built on Acronis Cyber Protect Cloud.

Where Microsoft's responsibility ends

Microsoft is responsible for the platform's uptime and the built-in security features working as documented. Configuring those features correctly for an accounting firm's specific risk profile, licensing the right tier, and monitoring for misuse are IT provider responsibilities. Our Microsoft 365 support services are built specifically around this configuration and monitoring layer for firms handling sensitive client data.

Sources and further reading

• Microsoft Learn: Microsoft 365 Business Premium security features

Frequently asked questions