How long should a cold email subject line be?

Under about six words. Short lines also read better on a phone.

Should I personalize the subject line?

Yes, with something true, like their product or a page. A merge tag alone is not personalization.

Do subject line tests need a lot of emails?

A few hundred per version gives a rough signal. Fewer than that, treat results as hints.

Cold Email Subject Lines for SaaS: What to Write and What to Avoid

What makes a subject line work

1Under 6 words
2Names something real
3Sounds like a person
4No hype or caps
5Test two versions

The short answer: keep it under six words, name something true about the company, and write it the way a colleague would. Skip hype, caps and fake replies. Test two meaningfully different lines on at least a few hundred contacts each and judge by replies, not opens.

What a good subject line does

It earns the open without promising something the email does not deliver. A reader decides in a second, so it has to look like mail from a person, not a campaign.

Examples you can adapt

Here are patterns that read as human:

Patterns that work

A question about [their product or page].
Your [specific page] and [one detail].
Saw your launch on [place].
Quick idea for [their team].
Who handles [the problem] at [company]?

What to avoid

Do not use all caps, exclamation marks, "Re:" or "Fwd:" on a first email, or words like free, guaranteed or act now. They trigger filters and trust alarms alike.

How to test two versions

Send version A to one group and version B to another group of similar companies. Judge by replies after seven days, not opens, because some mail apps load images automatically and inflate open counts.

A worked example

Two lines for the same list: "a question about your pricing page" and "quick idea for your team". After a week the first got 9 replies from 300 emails and the second got 4. The founder keeps the first and writes a new challenger. She changes only the subject line, so she can trust the result.

See what a good reply rate is Follow up the right way

Where Touchbase fits

Touchbase finds companies that fit what you sell, says why each one fits, writes a plain first email for each that you approve before anything is sent, and handles replies and follow-ups. You choose who to write to and what goes out.

Find your first customers with Touchbase

Touchbase finds companies that fit what you sell, writes each first email for you to approve, and handles the follow-ups. It is free to start, with no card.

Start free

Questions

How long should a cold email subject line be?: Under about six words. Short lines also read better on a phone.
Should I personalize the subject line?: Yes, with something true, like their product or a page. A merge tag alone is not personalization.
Do subject line tests need a lot of emails?: A few hundred per version gives a rough signal. Fewer than that, treat results as hints.