You spend time carefully crafting the campaign, pick the perfect subject line, hit send, and then nothing happens. Open rates are lower than you expected. The instinct is to blame the copy or the timing. Before you rewrite anything, ask a different question first: did the email actually reach the inbox?
Email deliverability for small businesses is one of the most overlooked parts of email marketing. Inbox providers like Google and Microsoft do not simply deliver or block email. They make algorithmic decisions about where each message lands: primary inbox, promotions tab, or spam folder. Most of the signals they use have nothing to do with your subject line, and everything to do with the five points discussed below.
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The five things that affect inbox placement
These are not five separate problems you fix once and forget - they are interlinked. A clean list improves your engagement rate. Better engagement strengthens your sender reputation. Strong authentication makes reputation signals more credible to inbox providers. Getting all five working together is what separates businesses with consistent inbox placement from those constantly chasing their tail on open rates.
1. Technical authentication: SPF, DKIM, and DMARC
Most small businesses skip this step, particularly when getting started on a free trial; that is a significant mistake.
SPF (Sender Policy Framework) is a DNS record that declares which servers are authorised to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each message, allowing the receiving server to verify the email has not been tampered with in transit. DMARC is the policy layer: it tells inbox providers what to do when SPF or DKIM checks fail, and gives you access to reports about authentication failures from your sending domain.
Without these records in place, inbox providers treat your email as unverified. That does not guarantee a spam folder placement, but it removes one of the most important trust signals they rely on to distinguish legitimate senders from spam operations.
Every major email platform guides you through the technical setup. Transpond, Mailchimp, ActiveCampaign, and others all have domain authentication guides in their account settings. The process involves adding a few DNS records with your domain registrar and usually takes under 30 minutes. If you are setting up a new sending domain, do this before you send your first campaign. If you are already sending without authentication in place, add it now. The Transpond email marketing guide covers how this looks in practice for that platform.
2. Your sending domain and IP reputation
Your reputation as a sender is tied to the domain used in your From address and, in most cases, the IP address your emails are sent from.
If you are sending from a shared domain (a subdomain owned by your email platform rather than your own domain), your reputation is pooled with every other sender on that infrastructure. This means that one high-volume spammer on a shared IP can affect everyone’s inbox placement. On the upside, these shared IP adresses send a large volume of emails every day and generally have a good reputation with Google, Microsoft, etc.
Some providers offer a ‘dedicated server’ or ‘dedicated IP address’ for email sending, which can be beneficial because it solates your reputation so it reflects only your own sending behaviour. However, new sending domains start with no history. Inbox providers have never seen them before, so they extend no credit. If you start by sending 5,000 emails from a brand-new domain, expect spam folder placement on a significant portion. The correct approach is domain warming: begin with a few hundred sends to your most engaged contacts, then increase volume gradually over several weeks as your reputation builds with inbox providers.
3. List hygiene: hard bounces and inactive contacts
This is where many small businesses accumulate a slow-burning deliverability problem without realising it.
Hard bounces happen when an email address no longer exists. They damage your sender reputation immediately. Most platforms auto-suppress addresses after a single hard bounce, so that part is usually handled for you. The subtler issue is inactive contacts: people who are still valid addresses but have not opened or clicked anything in months.
Inbox providers use engagement ratios as a core quality signal. A list of 2,000 contacts where 40% regularly engage is a stronger reputation signal than a list of 8,000 where only 8% open anything. The larger list looks worse, not better, from a deliverability standpoint.
Before any major campaign, segment out or suppress contacts who have shown no engagement in the previous six months. If you have imported or inherited an email list from another source, apply extra scrutiny: old lists often carry high proportions of invalid and disengaged addresses that pull your engagement metrics down immediately after the first send.
4. Engagement signals
Every time a recipient opens your email, clicks a link, replies, or moves it from spam to their inbox, that is a positive signal to inbox providers about the emails you’re sending, and your sending reputation. Every time they delete it unopened, mark it as spam, or let it sit unread indefinitely, that is a negative signal.
The cumulative effect shapes where your future emails land. Low engagement on one campaign makes the next campaign slightly more likely to be filtered. This is the deliverability spiral: once you are landing in spam, even your engaged subscribers may never see your emails there, so engagement drops further, and the problem compounds.
Segmenting your list before each send is the most practical tool for breaking this cycle. By sending each campaign only to contacts who are likely to be interested in that specific message, you raise the engagement rate on every send. A 35% open rate on a targeted send to 500 contacts does considerably more for your sender reputation than a 10% open rate on a broadcast to 2,500.
5. Content signals
Content signals matter less than reputation and authentication, but they are still part of how spam filters evaluate your email.
Spam filters examine the ratio of images to text. A message that is mostly one large image with a single line of text follows a pattern commonly used by spammers to evade text-based filters. Aim for a reasonable balance: a few paragraphs of text, one or two images, and alt text on each image in case images are blocked.
Avoid URL shorteners in your links. Shortened URLs obscure the destination, which spam filters treat with suspicion. Use full URLs or your platform’s built-in link tracking instead. Excessive capitalisation, multiple exclamation marks in subject lines, and words like “FREE” remain spam flags, though their weight has reduced as reputation signals have become more dominant in filtering decisions.
Keep your call to action focused - emails with one clear next step tend to produce cleaner engagement signals compared to emails with five different links competing for attention. Higher click-through on a focused CTA is better for your deliverability than a diffuse engagement pattern across many links.
How to monitor your email deliverability
Most small businesses check open rates after each send and assume that covers deliverability, but it only covers part of it. Low open rates are a symptom. The causes are usually technical or behavioural, and often invisible unless you know where to look.
After every campaign, check your bounce and complaint rates in your platform dashboard. A hard bounce rate above 2% or a spam complaint rate above 0.1% (one complaint per 1,000 sends) signals a problem that needs addressing before the next campaign goes out.
Google Postmaster Tools is a free service that shows your sending domain’s reputation with Gmail specifically. It takes around 20 minutes to set up and gives you direct visibility into whether your emails are landing in inboxes, spam folders, or being rejected entirely. Given that a large proportion of any UK business contact list will include Gmail addresses, this is worth setting up early and checking regularly.
Watch your open rate trend across campaigns over time, not just in isolation. A sudden drop that is not explained by content or timing changes often signals a deliverability shift: your reputation has moved, and emails that previously landed in the inbox are now being filtered before recipients ever see them.
For benchmarks on what open rates, click rates, and conversion rates to aim for, the email marketing conversion rates guide gives realistic figures from a study of over 300 million emails and explains what they mean in practice for small lists.
If you use MailerLite, the MailerLite MCP integration lets you ask Claude to analyse campaign-by-campaign open rate trends across your account directly, without manual data exports.
For a real-world example of a complete domain reputation recovery, the case study on restoring email deliverability for a UK wealth management firm walks through the full six-phase process from diagnosis to automated lead nurture.
TL;DR
- Email deliverability for small businesses depends on five factors: authentication, domain reputation, list hygiene, engagement signals, and content.
- Set up SPF, DKIM, and DMARC before your first send. Every major platform walks you through this.
- Some platforms allow you to send from your own domain, not a shared platform subdomain. These domains need ‘warming up’ gradually.
- Remove or suppress contacts who have not engaged in six months before any major campaign.
- Segmentation raises engagement rates, which directly improves your inbox placement over time.
- Monitor bounce rates, complaint rates, and open rate trends after every send.
- Use Google Postmaster Tools for direct visibility into your Gmail reputation.
Not sure why your emails aren't landing?
We work with small businesses to review their Email Marketing and CRM setup. If your open rates have dropped or your campaigns feel like they are disappearing, get in touch.