Flagging marks an email for follow-up without moving it. It places a visual marker on the message so it stands out, and most email clients give you a filtered view of everything you've flagged so you can work through it separately from the rest of your inbox.
Gmail calls them stars, Outlook uses flags with optional due dates and task integration, Apple Mail uses colored flags. All three give you a filtered view to work from.
It works well as a triage tool when you check that filtered view regularly. If flags accumulate without being cleared, the list becomes another inbox rather than a shorter one. The rest of this guide covers how flagging works in Gmail, Outlook, and Apple Mail, and when it is and is not the right tool.
What flagging an email does
Flagging places a small visual marker on an email so it stands out from everything else. The message doesn't move. You can still find it exactly where it arrived. The flag is just a signal you've left yourself: this needs attention.
Most email clients give you a filtered view of flagged messages. That's where the feature becomes useful. Instead of scanning your whole inbox trying to reconstruct what needed a reply, you open the flagged view and work through it in one pass. The decision about what matters has already been made. You just have to act on it.
The feature earns its keep when you treat the flagged view as a genuine to-do list and work through it regularly. Add flags faster than you clear them and it becomes noise. For messages that don't need action but shouldn't be deleted, archiving is the more useful move.
The catch is that the filtered view is often buried. In Gmail it lives under Starred in the left sidebar. Outlook has a Flagged Mail search folder. Apple Mail creates a smart mailbox automatically. If you're not in the habit of opening that view, flags accumulate and the system stops working.
Gmail: Stars, not flags
Gmail doesn't use the word “flag,” instead opting for stars. Click the empty star icon next to a message and it turns yellow. All starred messages are accessible from the Starred section in the left sidebar, or by searching “is:starred” in the search bar.
If you go into Gmail Settings, you can unlock additional star types: colored stars, exclamation marks, question marks. Most people never touch this, and for good reason. A single star used consistently is easier to manage than a color-coded system you have to remember.
Gmail stars carry no reminders. Nothing prompts you to return. If you star a message on Monday morning and don't check the Starred folder before your next run of meetings, it waits silently.
Outlook: Flags with due dates
Outlook's implementation is more functional. When you flag an email, you can right-click the flag and assign a due date. The email becomes a task in your To-Do list and shows up in your calendar view. Flag something for tomorrow and it surfaces as overdue if you haven't dealt with it by end of day.
For anyone managing a high volume of external correspondence, this matters. A flag with a due date chases you. A flag without one just waits. The difference in practice is whether your follow-up system has any teeth.
Flagged messages are accessible through the Flagged Mail search folder. Right-clicking your inbox and choosing "Show Flagged Messages" is usually the fastest route, though the exact path varies by Outlook version.
Apple Mail: Color coding
Apple Mail gives you six flag colors: red, orange, yellow, green, blue, and purple. You assign the meanings. Some people use red for replies needed today, green for threads where they're waiting on someone else. Most use one color and ignore the rest.
Flagged messages collect in a smart mailbox in the sidebar, sorted by color when you've used more than one. No reminders are attached, same as Gmail, so the discipline of checking the flagged view has to come from you rather than the system.
Flagging vs. starring: What's the difference
Functionally, there’s very little difference between flagging and starring emails. Both mark a message for attention and both create a separate view. The meaningful difference is that Outlook ties flags to due dates and task lists, giving the feature actual consequence. Gmail and Apple Mail treat theirs as visual labels only. If you work across multiple clients, flag status doesn't always sync reliably between them.
When flagging actually helps
For an account manager or sales rep managing high volumes of client correspondence, flagging works well as a fast triage decision. You scan your inbox, flag anything that needs a real reply or action, and keep moving. The inbox is where you decide what work exists, not where you do it.
A systematic review of 25 years of email research, published in the Journal of Occupational and Organizational Psychology, identified regular triaging as one of four behaviors consistently linked to better email performance and lower work-related stress. The point is to make fast decisions about what needs attention so that when you do sit down to clear your flagged view, you're not also deciding what matters.
If you're flagging thirty emails a day and clearing ten, the system degrades. The flagged folder becomes as overwhelming as the inbox it was supposed to simplify.
When something else works better than email flagging
Flags are for action items; things you need to respond to or act on. They're the wrong tool for reference material. For an email with a contract attached or a thread you'll need to quote back later, it’s better to archive those with a label or move them to a folder. A flag on reference material dilutes the signal on the things that actually need a response.
For threads where you're waiting on someone else, a dedicated label tends to work better than a flag. "Waiting on Sarah's contract" and "I need to write this proposal" look identical in a flagged view. A Gmail label called Waiting, or a matching Outlook folder, separates them. You need to know which pile is yours to act on and which is someone else's to move.
If the flagged folder has grown to the point where it's stopped being useful, the underlying inbox organization probably needs attention rather than the flagging habit specifically. Email overload is real, and it’s a problem.
Why email flagging works better with an organized inbox
Flagging assumes the inbox arrives in a state that makes triage possible. For most people managing a high volume of client correspondence, it doesn't.
According to the Fyxer Admin Burden Index 2026, a survey of 5,000 UK and US office workers, the average office worker receives 29 emails per day requiring a response and spends 4.3 hours a day on email. At that volume, scanning everything before you can decide what to flag is where the time actually goes.
The flag is a good tool for what it does. The issue is what happens before you reach for it. Fyxer sits inside Gmail and Outlook and organizes your inbox before you open it. Priority emails land at the top. Everything else gets filed into categories that reflect how your inbox actually works. By the time you're looking at your inbox, the sorting has already happened. You can still flag, still manage threads the same way you always have. You're just not spending the first stretch of your morning working out what the day contains.
If a growing flagged folder is how you're keeping important client emails from disappearing, that's the problem worth fixing at the source.
