Fifty thousand is an approximate number. It might be closer to 55,000 at this point, spread across a dozen client campaigns over the past two years, targeting industries from manufacturing to professional services to SaaS. Each campaign taught me something. Some of those lessons were expensive.
Here's what actually works, based on real data, not theory.
The single biggest factor in whether someone opens your email is the subject line. Not your sender name (though that matters), not the time you send it (though that matters too), but the eight to twelve words that appear in their inbox preview.
The optimal length across our campaigns is 38 to 52 characters. Enough to say something specific, short enough to display fully on mobile. Once you pass 60 characters, open rates drop measurably.
The best-performing subject lines are specific and low-hype. "Quick question about your warehouse operation" outperforms "How we can help you reduce costs by 30%." The first sounds like a person. The second sounds like a pitch. People open emails from people. They delete emails from salespeople.
Some patterns that consistently perform: referencing something specific to the recipient's company or sector. Using lowercase (it signals informality, which signals a real person). Asking a short question. Mentioning a mutual connection or a relevant event. "Saw your talk at the logistics expo" has a 41% open rate for obvious reasons.
Patterns that consistently fail: ALL CAPS anything. Exclamation marks. "Re:" or "Fwd:" tricks (people see through these and it destroys trust). Emojis in B2B (maybe fine for consumer products, death for director-level outreach). The word "free." The word "offer."
This surprised me when I first saw the data, but it's held up across every campaign since. The first email in a cold sequence should contain zero links.
The reason is partly technical and partly psychological. Technically, emails with links are more likely to be flagged by spam filters, especially from a new sending domain. Every link is a potential risk signal. The fewer links, the better your deliverability on that crucial first touch.
Psychologically, a link is an ask. You're asking the recipient to do something before they've decided you're worth their time. A first email that simply introduces yourself, explains why you're writing, and asks a question feels like a conversation. A first email with three links to your website, a case study, and a booking calendar feels like an advertisement.
Save the links for email two or three, once you've established a reason for the recipient to be interested. The first email's only job is to get a reply.
Emails sent from "martin@aa2.co.uk" outperform emails sent from "info@aa2.co.uk" by roughly 28% in open rates and over 40% in reply rates across our campaigns. The difference is even larger for emails sent from "The AA2 Team" versus a named individual.
People reply to people. It's not more complicated than that.
This has implications for how you set up your sending infrastructure. Your cold email domain should be a personal-sounding address, not a generic one. The "from" name should be a real person's real name. The signature should have a photo, a phone number, and a one-line description. Everything about the email should signal "a human being typed this" rather than "a system generated this."
Mail merge is not personalisation. Dropping someone's first name into an email template is the bare minimum, and your prospects know it. When every automated email starts with "Hi Sarah," the personalisation means nothing because it costs nothing.
Real personalisation references something specific to the recipient that you couldn't have known without looking. Their company's recent expansion. A hire they just made. A problem specific to their industry sector. An event they attended or spoke at.
For a golf networking business we ran campaigns for, we personalised every email by the recipient's nearest group, local venue, and the name of their regional ambassador. Not just "Dear Sarah" but "I noticed you're based near the Leeds group, which meets at Oulton Hall." That campaign achieved open rates above 40% and reply rates that our generic version couldn't touch.
The cost of real personalisation is time. You can't personalise 10,000 emails individually, but you can personalise by segment. If you've built your data properly (scored, segmented by sector and geography), each segment gets messaging that feels personal because it addresses their specific context.
Sending 5,000 cold emails from a brand-new domain on day one is the fastest way to get blacklisted. I know this because I've seen clients try it before working with us.
Domain warming means gradually increasing your sending volume over two to four weeks. Start with 20 emails per day to engaged contacts (people who'll open and reply). Increase by 20 every few days. Build a positive sender reputation before you scale.
We set up dedicated sending domains for every client campaign. Not their primary business domain (if that gets blacklisted, their regular email stops working) but a related domain that's clearly connected. If the company is acme-engineering.co.uk, the sending domain might be acme-engineering.com or acme-eng.co.uk. SPF, DKIM, and DMARC records configured before the first email goes out.
The warming process is tedious. There's no shortcut. But the alternative is your carefully crafted emails landing in spam folders where nobody will ever see them.
Tuesday through Thursday, between 7:30am and 9:30am, consistently outperforms every other time slot across our campaigns. Friday afternoons are dead. Monday mornings are cluttered. The early morning window catches people during inbox triage, when they're making quick decisions about what to read and what to delete.
Sequence length matters too. Three emails is the minimum for a cold sequence. Five is optimal for most B2B campaigns. Beyond five, you're in diminishing returns territory for cold outreach (warm nurture sequences can run longer).
The spacing between emails should increase. Email two arrives three days after email one. Email three arrives five days after email two. Email four arrives seven days after that. Each email should add something new, a different angle, a piece of content, a specific result. Sending the same "just checking in" message four times isn't a sequence. It's spam.
Cold email doesn't produce instant results. The first campaign for any new client typically performs worse than the third. The data gets cleaner with each send (bounces removed, non-responders deprioritised, engaged contacts identified). The messaging gets sharper as you learn what resonates with that specific audience. The sending reputation strengthens as your domain history builds.
The businesses that succeed with cold email are the ones that treat it as an ongoing programme, not a one-off blast. Build the data properly, warm the domain, test the messaging, iterate based on results, and keep going. Fifty thousand emails later, the process is dialled in. But it started with the first fifty.
Martin Dugan, AA2
