Think of the subject line as the one (short) sentence sales pitch for you message.
Explain what's in your email that is worth reading.
Good subject lines promise to save time or money, solve a specific problem, quantify benefits, use humour, include the recipient’s name, create mild disbelief and a sense of urgency to turn recipients into readers.
Here are some examples:
This is how Joey saves 40 minutes a day on admin tasks
Check out our featured destinations, 20% off this week only
{fname}, do you need more donors? (view merge field options)
File your taxes headache-free. No way?
Some bad examples:
[company name] newsletter
Boring, nothing in here to entice readers to openRe: some topic
Faking a reply by using "Re:" is just that...it's a fake and your readers will knowALL CAPS
This is plain rude
Length of subject lines
Remember that in many inboxes subject lines get trimmed after about 40 or so characters. The technical limit is 120 characters using Envoke.
Emojis in subject lines?
It greatly depends on your audience and support by email clients. Read more here.
Subject lines are not alone
The pre-header content of your email is an extension of the subject line. Always think of them together and make sure they complement each other. Read more about pre-header content here.