Copilot vs ChatGPT for Email: Outlook, Gmail, and the Graph Advantage
Copilot wins inside Outlook, full stop. Here is why, and when ChatGPT still wins elsewhere.
The Outlook Graph Advantage
M365 Copilot in Outlook reads data from your Microsoft Graph automatically when you ask it to draft or reply to an email. This includes your inbox history with the specific contact (all prior exchanges), your shared calendar (to check meeting context), your organisation chart (to understand the reporting relationship), your recent Teams conversations with that person, and any sensitivity labels on attached documents.
ChatGPT has none of this unless you manually paste it. For a simple email to a stranger, both are equally capable. For a contextually nuanced reply to someone you have been working with for months, Copilot’s Graph access is a meaningful advantage that no amount of prompt engineering can fully replicate.
Task-by-Task: Email in Outlook
Copilot summarises the thread and drafts a reply in context. ChatGPT requires you to paste the entire thread.
Copilot summarises any thread directly inside Outlook with one click. ChatGPT requires manual export and paste.
Copilot knows the recipient from your Graph data. ChatGPT is competitive if you provide the context manually.
Copilot reads your calendar and the recipient's calendar (if shared) to suggest availability and draft scheduling emails.
Both are equally capable for a quick, low-context reply. Copilot's tone presets (friendly, formal, concise) are a minor convenience.
ChatGPT wins for mail merge and bulk personalised emails via API or custom GPT for variable substitution at scale.
ChatGPT wins for Gmail. Copilot has no Gmail integration. Gemini integrates natively with Gmail for Google Workspace users.
Tone and Style Presets
Copilot in Outlook has built-in tone presets: friendly, formal, concise, and a few others. For users who write many emails in different registers throughout the day, these presets are a workflow convenience that avoids having to prompt for tone every time. ChatGPT has equivalent capability (just ask “rewrite this more formally”) but requires a separate prompt step rather than a single click.