How to Write Effective Email Subject Lines That Get Opened (SIS Principle)

You write a perfect email. You spend 20 minutes on it. You hit send.

And no one opens it.

Why? In 90% of cases, the problem is not your email — it’s your subject line.

In business today, your inbox is a battlefield. The average professional receives 60-100 emails a day. Managers receive 200-300, and executives get 500-700 emails a day.

If your subject line doesn’t grab attention in 3 seconds, your email will be deleted, ignored, or lost forever — no matter how important your message is.

Let’s fix that with a simple system.

What Is a Subject Line?

Every email has 3 parts:

1. To: The recipient’s email address
2. Subject Line: A short summary of WHY you are writing
3. Message: The body of your email

The subject line is the ONLY part people see before deciding to open or delete. On mobile, they see just 3-5 words (25-30 characters). On desktop, 5-7 words (about 50 characters).

That is your one shot.

5 Useless Subject Lines That Kill Your Email

If you write like this in a business context, your email will almost certainly stay unopened:

• Hi / Hello / Good morning, how are you?
• Re: (with nothing after it)
• Ref / Reference
• Dear Fred / From Mary (they already know who it’s to and from)
• (No Subject)

These tell the reader NOTHING. They create work for them.

The SIS Principle: The Easy Formula That Works

The secret to a subject line that gets opened is SIS — Short, Informative, Specific.

Don’t write three different lines. Think through these three filters to create ONE perfect line.

S – Short: What is the key word?
I – Informative: Add more detail — which one, where, when?
S – Specific: What is the action or status?

How it works in real life:

Example 1: A meeting is cancelled

• Short: Meeting
• Informative: June 7th Meeting
• Specific: Cancelled: June 7th Meeting

From useless to instantly useful.

Example 2: You want a refund from Amazon

• Short: Order
• Informative: Amazon Order #625
• Specific: Refund Request: Amazon Order #625

Now Amazon knows exactly which department to send it to, and can find your order instantly.

Example 3: You need to meet your professor

• Short: Appointment
• Informative: Requesting Appointment
• Specific: Req. Appt to Discuss Thesis - John Grant

Pro Tip: Use common abbreviations to save space: Req. = Requesting, Appt = Appointment, Mktg = Marketing, Conf = Conference. On mobile, every character counts.

10 Ready-to-Use Templates by Situation

1. Applying for a job (if not specified in ad):

• Short: Job
• Final: Application: French Teaching Job #52 - Anna Smith
• Important: Always check the job ad first — if they tell you what to write in the subject, write EXACTLY that.

2. Conference:

• Confirming Attendance: Mktg Conf. - May 15
• Attending Mktg Conf.?

3. Sending a resume (unsolicited):

• Receptionist Resume: John Grant
• Exception: Always put your name when sending a resume so it can be found.

4. Customer Service / Order Issue:

• Refund: Amazon Order 625 - Damaged Bowl
• Inquiry: Order #8821 - Delivery Status

5. University / Academic:

• Thesis Meeting Request: This Week?
• Question re: Assignment 3 - ENG 101

Power Vocabulary for Subject Lines

Save this list. These verbs and nouns make your subject line sound professional and searchable.

Power Verbs (use with a colon):

• Cancelled: The event will not happen
• Postponed: Delayed to a later date/time
• Confirmed / Booked: Reserved, secured
• Shipped / Delivered: Sent / Arrived
• Requested: You are asking for something
• Rescheduled: Time/date changed
• Approved: Someone said yes
• Action Required: Needs their immediate action

Power Nouns:

• Arrival, Interview, Introduction, Referral, Follow-up, Inquiry, Proposal, Update

Examples:

• Postponed: Team Meeting to Thursday 3PM
• Introduction: Sarah Lee / David Chen
• Follow-up: Interview Jan 20 - Thank You
• Proposal: New Website Design - Q3 Budget

5 More Rules for Subject Lines That Get Opened

1. Don’t abuse “Important” or “Urgent”
Use it only when it truly IS urgent. If every email is urgent, none are.

2. NO ALL CAPS
Writing IMPORTANT MEETING CANCELLED feels like you are shouting. It’s rude and spammy.

3. Update the subject when replying
If you start with Proposal and now you are talking about the Marketing Conference, CHANGE the subject line. Otherwise your important email will be lost in a thread of 17 “Re: Re: Proposal” emails.

4. When to write it?
Write it BEFORE you write the email to stay focused, then double-check it AFTER you finish to make sure it still matches what you wrote.

5. Keep it searchable
Think: How will this person search for this email in 3 months? Put the order number, date, or project name in the subject.

Your Next Step

Go to your Sent folder. Look at your last 5 subject lines.

Would YOU open them if you had 300 emails in your inbox?

Rewrite them using SIS — Short, Informative, Specific — and you will see your response rate go up immediately.

What is the hardest subject line you have to write at work? Write it in the comments and we’ll fix it with SIS!