You can write the best message in the world but if the subject line spooks a filter, no one ever sees it.
Most recruiters don’t realise how many “harmless” patterns look risky to spam filters. It’s not just about keywords anymore. It’s punctuation, tone, and predictability.
The good news: you can fix this in ten minutes.
The truth in plain sight
Filters don’t read your subject line like a human does.
They scan it for patterns that usually mean spam, scams, or over-eager marketing.
Here are the red flags that make filters twitch:
- Odd punctuation. ?!, multiple !, or ellipses (…) often signal “attention-grabbing” spam.
- Inconsistent capitalisation. Subject lines that shout (READ THIS NOW) or switch case (Great Offer TODAY) get flagged.
- Over-promising words. “Guaranteed”, “Free”, “Exclusive access”, “Act fast” all still trigger thresholds when combined with tracking links.
- Cluttered formatting. Emojis, brackets, and ALL CAPS are fine in moderation… but stack too many and it looks fake.
How filters actually decide
Modern spam filters weigh signals rather than single words:
- Language behaviour – unusual punctuation, salesy tone, or random capitalisation.
- Engagement history – if previous campaigns were deleted unopened, filters tighten the gate.
- Authentication quality – if SPF, DKIM, or DMARC fail, your subject line has to fight uphill.
- Link structure – if your links are rewritten through tracking domains, you’re already on thin ice.
A safe subject line can’t rescue broken authentication, but it can keep good mail looking clean. There are a million ways of writing a good subject line, and they should always lean towards being compelling and/or honest. In this article, we focus on super-filter-friendly advice to get you on the right track, but you always A/B test your email outreach to see what works best for your audience.
What to do
1. Keep it conversational
Try writing it like you’d send a personal note:
- “Quick question about your developer role”
- “Follow-up on our chat last week”
- “Are you still hiring in Bristol?”
These feel human because they’re grounded in context, not copywriting tricks.
2. Watch the punctuation
Use one punctuation mark at a time.
- Good: Question about your data engineer brief?
- Risky: Question about your data engineer brief?!
Avoid leading or trailing punctuation:
- Don’t start with ! or end with …
3. Test before you send
Before every campaign, drop a few test emails into personal inboxes across Gmail, Outlook, and iCloud.
If one consistently hits junk, tweak your subject and resend.
Sometimes one character change is enough to tip the balance.
4. Stop keyword stuffing
You don’t need “Hiring”, “Urgent”, and “Limited” all in one line.
Filters value consistency. Reuse safe, honest patterns that generate replies, not clickbait.
5. Re-engage gently
When recontacting old lists, avoid hype.
Subject lines like “Just checking in” or “Still relevant?” outperform “We miss you!” because they feel natural.
Inbox Test
Take a look at the results of previous campaigns.
List the subject lines and count how many contain !, ?, or ….
Compare the results with other campaigns and see if the style of some might be signalling spammy intent to filters.
Reality check
There’s no “magic subject line” that guarantees inboxing.
Deliverability depends on the combination of technical health, sending behaviour, and language hygiene.
But clean, calm subject lines make it much easier for your other improvements to work.
Learn more
Wnat to hear more about this? In this Amplifying Recruitment podcast Ben Fielding breaks down the tiny language signals that separate trustworthy recruiters from spam folders.
Next sensible step
Messy metrics? Quinset highlights the technical blockers so your subject-line fixes actually land.
Or book a 30-min discovery call with Ben Fielding, and let him know what’s working and, more importantly, what isn’t. He’ll build you a strategy that drives more messages to inboxes, not junk.
