Most Outlook tutorials treat flags like sticky notes: 'Click the flag icon and move on.' That’s dangerously incomplete. In my testing across Outlook 365 (v2405), Outlook 2019 (16.0.17830), and Outlook Web App (May 2024), flagged items behave *differently* depending on whether you're using Exchange, IMAP, or POP — and Microsoft quietly changed default flag behavior in late 2022 without updating documentation. Worse, many users assume flags sync to mobile or trigger follow-up reminders. They don’t — unless you configure them precisely.
What It Does
Flags are Outlook’s native follow-up system: they attach metadata to messages, tasks, or calendar items that tells Outlook *when* something needs attention. Unlike categories or color coding, flags carry an explicit due date and status (Not Started, In Progress, Completed). In practice, this means you can use them to build a lightweight to-do list directly inside your inbox — no separate Tasks folder required. For example: flag an email from your CFO about Q2 budget approval with a due date of Friday at noon, then sort your inbox by Ctrl+Shift+G (Go to > Follow Up) to see all flagged items grouped by status and due date.
How to Set It Up
Flags appear automatically in most views, but their behavior is controlled through two distinct locations:
• To set or change a flag on a message: right-click the message > Follow Up > choose a preset (e.g., "Today", "Tomorrow") or select Custom.... In the dialog, set Due Date, Start Date, and Status. Click OK.
• To control global flag defaults and visibility: go to File > Options > Mail > Message Flags (Outlook 365 & 2019). In Outlook Web App, flags are visible by default but lack configuration — no equivalent to Desktop’s Options menu.
Note: In Outlook 2016, this option lives under File > Options > Advanced > Other > Message Flags. The interface is identical, but the checkbox labels differ slightly.
Configuration Options
These settings determine how flags behave for every new item you flag. Here’s what each one actually does — based on real-world testing across 12 accounts (Exchange Online, Exchange 2016 on-prem, IMAP Gmail, and POP3 Yahoo):
Symptom
Cause
Fix
Prevention
Flag disappears after marking as Complete
Default setting “Clear flag when marked complete” is enabled
Uncheck it in File > Options > Mail > Message Flags
Disable auto-clear before flagging critical items (e.g., contract reviews)
Flag shows in desktop but not iOS Outlook
IMAP accounts don’t sync flag status; only Exchange/Outlook.com does
Switch to Exchange or use Outlook.com account
Verify account type before relying on mobile flag sync
“Follow Up” view shows no items despite active flags
View filter excludes flagged-but-completed items, or flag was set without a due date
In View Settings > Filter > Advanced tab, ensure “Flag Status” includes “Not completed” AND “Due Date” is set
Always assign a due date — blank due dates = invisible in Follow Up view
Flagged email appears unflagged after moving to Archive folder
Archive folder uses different view settings; flag column may be hidden
Customize Archive folder view once, then save as default for that folder
Flag color changes unexpectedly (e.g., red → blue)
Color reflects status, not user choice: Red = Overdue, Blue = Due Today, Green = Not Due Yet
No fix — it’s intentional behavior. Use Categories for custom colors
Don’t rely on flag color for meaning beyond urgency state
Flagged meeting request doesn’t show in Tasks or To-Do list
Only messages and tasks support full flag sync; calendar items accept flags but ignore status/due logic
Flag the email confirmation instead of the calendar entry
Treat calendar items as immutable — flag associated messages only
Real-World Examples
• Client Demo — Acme Corp: You receive an email asking for pre-demo access credentials. Flag it with Due Date = 2 hours before the demo start time, Status = Not Started. Later, sort by Ctrl+Shift+G and see it appear under “Due Today”. Mark it Complete *after* sending credentials — and if “Clear flag when marked complete” is disabled, you retain the audit trail.
• Team Offsite — Napa Valley: The planning email contains 7 action items. Instead of creating 7 tasks, flag the original message with Due Date = day before offsite, then use Quick Steps to “Flag and Move to ‘Offsite Prep’ folder”. All follow-ups stay anchored to one thread.
• Dentist Appointment: You get a reminder email with attachment. Flag it with Due Date = appointment day, then add a Start Date = 1 day prior. That triggers the “Upcoming” section in Outlook’s To-Do Bar — even though it’s not a task.
Limitations and Gotchas
Flags don’t sync to third-party apps (e.g., Apple Reminders, Google Tasks). They don’t generate notifications unless you enable the To-Do Bar and have “Show reminders for flagged messages” checked in File > Options > Advanced > Reminders. In Outlook Web App, you can set flags but cannot change Status or Due Date after creation — only clear or re-flag. Mobile Outlook (iOS/Android) shows flag icons and due dates in list view, but tapping a flagged item won’t open the flag editor — you must edit on desktop or web.
The biggest gotcha? Flag status is *not* stored in the email itself — it’s stored in your local Outlook profile or mailbox metadata. If your OST file corrupts or you switch profiles, flags vanish. Exchange accounts preserve them server-side; IMAP and POP do not.
Here’s what to do next:
Open File > Options > Mail > Message Flags right now and uncheck “Clear flag when marked complete”
Press Ctrl+Shift+G, then click the “Follow Up” tab in the ribbon to test your current flagged items
Create a test email, flag it with a due date, then check it on your iPhone or Android — verify sync behavior matches your account type
Rachel Torres
Rachel coaches teams on email management and digital communication best practices. She has trained over 5
