What makes a follow-up email urgent?
A follow-up is urgent when there is a real deadline the reader would care about, and something changes for them if it passes. If the only deadline is your own target, write a normal follow-up instead: urgency the reader can’t see reads as pressure. Use this table to decide:
| Situation | A real deadline for them? | What to send |
|---|---|---|
| A signature or approval needed to keep a start date | Yes | Urgent follow-up with the date, the time zone and what moves if it’s missed |
| Information from a client that work is waiting on | Yes | Urgent follow-up that names the slip and offers a fallback |
| A price or quote that expires on a set date | Yes, if the expiry is real | One heads-up before the date, then one on the day |
| A decision from a colleague that blocks you | Yes | A yes-or-no request with your default if you don’t hear back |
| A payment or bank detail question | Often | Short email, then confirm by phone on a number you already have (see the phishing section below) |
| Your month-end or quarter-end target | No | A normal follow-up; our guide to following up when they say check back next quarter covers timing |
A cold prospect who hasn’t replied isn’t urgent either. Google’s email sender guidelines, written for mail sent to personal Gmail accounts, say message subjects and headers should accurately represent the sender and the content and shouldn’t be misleading; in our reading, a made-up deadline in the subject fails that test. For prospects, use the timing in our guide to cold email follow-ups.
How do you write an urgent follow-up email?
Put the action and the deadline in the first line, then the consequence, then make the action as small as possible. Six parts, in this order:
- The ask and the deadline. One action, with a day, a time and their time zone: by Thursday at 5pm your time.
- What happens if it’s missed. One true sentence: the start moves to the 15th; we launch with placeholder images.
- Everything they need to act. The page to sign, the question to answer, the file you need. Point to where it already is in the thread.
- A way out. If they can’t do it in time, what is the next best thing? Ask them to pick.
- A faster channel. Your phone number, or a time you will call.
- Nothing else. No second request, no catch-up news, no apology for writing again.
Then decide on the subject line. Gmail’s help page on conversations says a conversation breaks off into a new conversation when the subject line changes. That gives you two options:
| Option | Use it when | What to do |
|---|---|---|
| Reply in the thread, same subject | The thread is recent and the subject still says what it’s about | Start the first line with the deadline |
| Reply with a new subject | The thread is weeks old, or the subject hides what you need | Put the action and date in the subject, and restate the context in two lines, since the reader may see it as a new conversation |
How long should you wait before following up on an urgent email?
For most urgent requests, wait about one working day, then send one short nudge, and switch to a call or text once half the remaining time has gone. The one-day mark comes from a 2015 study of Yahoo Mail by Farshad Kooti and colleagues, presented at the WWW 2015 conference. It covered more than 2 million opted-in users exchanging 16 billion emails over several months, and looked at replies between pairs of users who had each sent at least five replies to the other. More than 90% of replies came within a day of the message, half within 47 minutes, and the single most likely reply time was two minutes. These are people who already write to each other, as in an urgent follow-up to someone you already work with; it says nothing about people who never reply, and the data comes from Yahoo Mail accounts in a paper published in 2015, so treat it as a rough guide.
The halfway rule is our own; the study doesn’t make it. Here it is in a worked example with sample names. Northwind Ltd needs Priya at Acme to sign an order form by Thursday at 5pm Priya’s time. Northwind is five hours ahead. It is Tuesday at 9am for Priya, and we count working hours as 9am to 5pm:
- Working hours left: Tuesday 8 + Wednesday 8 + Thursday 8 = 24.
- Halfway point: 24 ÷ 2 = 12 working hours, which is Wednesday at 1pm for Priya (8 hours on Tuesday, then 4 more).
- One-day mark: Wednesday at 9am, 24 clock hours after the email.
| Priya’s time | Northwind’s time | Working hours left | What Northwind sends |
|---|---|---|---|
| Tuesday 9am | Tuesday 2pm | 24 | The urgent follow-up (template 1 below) |
| Wednesday 9am | Wednesday 2pm | 16 | A one-line nudge in the same thread |
| Wednesday 1pm | Wednesday 6pm | 12 | A call, then a text if there’s no answer |
| Thursday 9am | Thursday 2pm | 8 | The deadline-day note (template 5) |
| Thursday 5pm | Thursday 10pm | 0 | Do what you said would happen |
With a deadline of less than a day, skip straight to the call after the first email. For follow-ups with no deadline at all, our guide to following up without being annoying uses widening gaps instead.
How can I flag an email as urgent?
In Outlook you can mark a message High Importance; in Gmail, the importance marker is set by Gmail for the reader. The steps below are from each help page, checked 4 November 2026, and cover Outlook and Gmail on a computer.
Classic Outlook
In a new message or a reply, select High Importance on the Message tab. If you don’t see it, select the ellipsis, then High Importance in the Tags section, according to Microsoft’s help page. The recipient sees a red exclamation point in the Importance field in their inbox.
New Outlook
The same page says to open the Options tab in a new message or reply, select Importance and pick the level; it lists Outlook on the web among the versions it applies to. A second Microsoft importance page, for Outlook for Microsoft 365, 2024 and 2021, adds that in most email programs, recipients see a special indicator in the message list or headers.
A reminder for the recipient
In classic Outlook for Microsoft 365, Microsoft’s reminder page says to select Message, then Follow Up (or Tags, then Follow Up, if you only see Tags on the ribbon), then Add Reminder, and enter the date and time for a reminder dialog box that the recipient will receive.
Gmail
Gmail’s importance markers page says Gmail decides which emails to mark important from signals such as whom the reader emails and how often, and which emails they open and reply to. The page describes the reader’s settings and no option for the sender. In Gmail, the deadline in your first line is the flag.
Remind yourself in Gmail
Turn on follow-up nudges: Settings, See all settings, the General tab, then next to Nudges select Suggest emails to follow up on, and Save Changes. Gmail’s help page says nudges need conversation view turned on.
Keep the flag for messages that meet the table at the top. The same Google sender guidelines list URGENT REQUEST among the display names not to use, and say a display name should identify the sender and leave out subject or message content.
Why can an urgent email look like phishing?
Because urgency is one of the signs people are taught to distrust. Gmail’s phishing help page tells users to beware of urgent-sounding messages that appear to come from people they trust, such as someone from work, and to check by contacting that person through the details they normally use. A CISA phishing page (now in CISA’s archive) lists urgent or emotionally appealing language, especially messages that claim dire consequences for not responding immediately, as a common sign.
An urgent request for a signature, a login or a payment has the same shape as a phishing email, so make yours easy to trust:
- Refer back to the thread. Reply where the document already sits instead of sending a new link.
- Name something only you would know. The order form from Monday’s call, the invoice number, the person who asked for it.
- No new bank details by email. If payment details have changed, say so and ask them to confirm by phone on a number they already have.
- No surprise attachments. If you must attach something new, say what it is and why in the first line.
- Make the consequence plain. The start date moves; nothing about accounts being closed or penalties you can’t point to.
Urgent follow-up email templates you can copy
Five templates for a small B2B team. Northwind Ltd, Priya and Sam at Acme are sample names; replace every bracket, and only state a deadline or consequence that is true.
If the urgent item came out of a call, send the recap the same day so the deadline is in writing; our guide to following up in the first 24 hours after a sales call has that email. For booking links, Siela’s calendar and booking pages are checked against every connected calendar and send reminders. For follow-ups with no deadline, our 16 follow-up email templates cover each stage.
This week: pick one open item with a real deadline, work out its halfway point in the reader’s working hours, and put the call in your calendar before you send the email.
Frequently asked questions
How do I politely remind someone to respond to an email?
Reply in the original thread and keep the subject, since Gmail’s help says a changed subject line starts a new conversation. Make the first line the one thing you need and the day, for example: could you confirm the order form by Thursday at 5pm your time? Offer a yes or no, or two options. With no real deadline, wait two to three days and add one new fact.
How do you email someone after a long time professionally?
Open with why you are writing now, then one line that places you, such as the project and the year (for example: we worked together on the Acme rollout in 2023). If the old thread is long, start a fresh email with a subject that says what you need; Gmail treats a new subject as a new conversation, so restate the context in two lines. Then ask for one small thing.
Is it rude to write urgent in an email subject line?
It isn’t rude when the deadline is real, but the word alone tells the reader little. A subject such as Signature needed by Thu 5pm ET says what is urgent and when. Google’s sender guidelines list URGENT REQUEST among display names to avoid, and its phishing help warns users about urgent-sounding messages, so specific beats loud.
Should I call or email when something is urgent?
Email first when the reader needs the details in writing, such as a document to sign, then call once half the time to the deadline has gone with no reply. Under a day from the deadline, email and call together. For anything involving payment details, confirm by phone on a number you already have before anyone acts on the email.
What can I say instead of ASAP?
Give a day, a time and the reader’s time zone, plus the reason: by Thursday at 5pm your time, so we keep the start date. ASAP leaves the reader to guess how urgent you are, and different readers guess differently. If you genuinely need it within hours, say the hour and call as well as emailing.
Sources
- Kooti, Aiello, Grbovic, Lerman, Mantrach: Evolution of Conversations in the Age of Email Overload (arXiv 1504.00704, WWW 2015) (submitted 2 Apr 2015, checked 4 Nov 2026)
- Microsoft Support: Mark a message as important (checked 4 Nov 2026)
- Microsoft Support: Mark a message as high or low importance in Outlook (checked 4 Nov 2026)
- Microsoft Support: Add a reminder to an outgoing message (checked 4 Nov 2026)
- Gmail Help: Importance markers in Gmail (checked 4 Nov 2026)
- Gmail Help: Reply to messages in Gmail (nudges) (checked 4 Nov 2026)
- Gmail Help: Group emails into conversations (checked 4 Nov 2026)
- Gmail Help: Email sender guidelines (checked 4 Nov 2026)
- Gmail Help: Avoid & report phishing emails (checked 4 Nov 2026)
- CISA: Recognize and Report Phishing (archived content) (checked 4 Nov 2026)