What is the difference between an ISP and a mailbox provider?

ISPs provide internet access, while mailbox providers offer email services. Often, an ISP can also be a mailbox provider (e.g., BT offering BT Mail to its broadband customers). For email deliverability, both are important as ISPs route traffic and MBPs handle inbox placement.

What affects email deliverability to UK mailbox providers?

Key factors include sender reputation (based on engagement, spam complaints), email authentication (SPF, DKIM, DMARC), and content quality. Being on a blacklist or blocklist will also severely impact delivery.

How can I determine the mailbox provider for an email address?

You can use various online tools or manual DNS lookups to find out the mailbox provider associated with an email address or domain, typically by checking its MX records.

Do UK mailbox providers offer feedback loops?

Major providers like Google (Gmail) and Microsoft (Outlook.com) offer Feedback Loops (FBLs) . These notify senders when recipients mark their emails as spam, which is crucial for managing list hygiene and maintaining a good reputation.

What are the top ISPs and mailbox providers in the UK? - Technical - Email deliverability - Knowledge base

Understanding the landscape of internet service providers (ISPs) and mailbox providers (MBPs) in the UK is crucial for anyone involved in email marketing or deliverability. The market is dynamic, with both global giants and significant local players shaping how emails land in inboxes. For effective email campaigns, knowing who the key gatekeepers are can make a substantial difference.

While ISPs primarily provide internet access, many also offer email services, acting as mailbox providers. This dual role means that deliverability strategies need to consider both the network infrastructure and the specific email filtering mechanisms in place. It’s not just about getting to the server, but about getting past their spam filters.

Leading UK internet service providers

When we talk about leading ISPs in the UK, we're primarily looking at the major broadband providers with the largest subscriber bases. These companies form the backbone of internet access for millions of households and businesses. Their infrastructure and policies can indirectly influence how emails sent to their users are treated, even if those users access email through a different mailbox provider.

BT Group, encompassing BT, Plusnet, and EE, holds a significant portion of the market, with millions of subscribers. Virgin Media and Sky Broadband also stand as major players, competing closely for the top spots. TalkTalk rounds out the primary group of large-scale providers. These providers not only offer internet connectivity but often integrate email services into their packages, making them important mailbox providers as well.

Understanding the market share of these ISPs can give us an idea of the volume of email traffic they handle. For instance, data indicates that BT, EE, and Plusnet combined lead in terms of broadband customers in the UK. This dominance means that maintaining a good sender reputation with their systems is paramount for deliverability.

Provider	Primary Service	Significance
BT Group	Broadband, TV, Phone	Largest market share, includes Plusnet and EE.
Virgin Media	Broadband, TV, Phone	Significant market presence, known for high speeds.
Sky Broadband	Broadband, TV, Phone	Major player with extensive customer base.
TalkTalk	Broadband, Phone	Competitive player in the broadband market.

Prominent UK mailbox providers

Beyond the pure internet connectivity, mailbox providers are the direct gatekeepers of the inbox. Globally, Gmail, Yahoo Mail, and Outlook (Microsoft) dominate the email landscape, and this holds true for the UK as well. Many UK users access their emails through these major international providers. Therefore, ensuring your emails are well-received by Outlook.com and Gmail's systems is paramount.

Alongside these global giants, there are also significant UK-based or UK-focused mailbox providers and hosting services. For example, Microsoft (including Outlook.com and Exchange Online) and Google remain dominant. IONOS and 123 Reg are notable hosting and email providers that serve a substantial UK customer base. Even providers like BT Mail, often used by BT broadband customers, are important to consider.

Key UK mailbox providers

Understanding the email services your UK audience uses is crucial. While major free email providers like Gmail and Outlook are widespread, don't overlook regional or ISP-specific email addresses.

Provider types: Mailbox providers directly receive and filter emails. ISPs provide internet access, and some also offer email services.
Deliverability impact: Each mailbox provider has its own filtering rules, which can vary significantly in strictness and criteria.

Navigating deliverability across providers

Deliverability to these providers, whether large global players or smaller UK-focused entities, isn't uniform. Each has its own set of algorithms and metrics to determine if an email reaches the inbox, the spam folder, or is outright blocked. Factors like sender reputation, email content, and authentication are all weighed heavily.

Many smaller ISPs and even some larger ones in the UK outsource their spam filtering to third-party providers. You might encounter providers like Cloudmark, Proofpoint, or Mimecast acting as the actual filtering engines behind many UK mail domains. This means your email might be passing through multiple layers of scrutiny before reaching the recipient.

For good deliverability, understanding the specific requirements of each major provider is key. This often involves monitoring your sender reputation, responding to feedback loops, and ensuring proper email authentication. Tools that can identify the mailbox provider for a given email address are very useful for this purpose.

Global mailbox providers

Volume: Handle massive volumes of email, with sophisticated filtering systems.
Metrics: Heavily rely on user engagement, spam complaint rates, and authentication for domain reputation.
Feedback loops: Offer feedback loops (FBLs) to ESPs for spam complaints.

UK-specific and smaller providers

Volume: May handle lower volumes, potentially relying on third-party filters.
Metrics: Can be more sensitive to local spam trends and smaller blocklist (or blacklist) impacts.
Feedback loops: Fewer offer FBLs, making direct feedback challenging.

Blocklists, authentication, and sender reputation

Email deliverability relies heavily on maintaining a clean sender reputation. Being listed on a blocklist (or blacklist) can severely impact your ability to reach inboxes, not just in the UK but globally. Many ISPs and mailbox providers, including those in the UK, consult various public and private blocklists to filter incoming mail.

Proper email authentication, including SPF, DKIM, and DMARC, is no longer optional, it’s a requirement. Major providers in the UK and worldwide use these standards to verify sender legitimacy. A misconfigured DMARC record or a missing SPF record can lead to emails being rejected or sent straight to spam. Here’s a basic DMARC record example:

Example DMARC recordDNS

v=DMARC1; p=none; fo=1; ruf=mailto:forensic@yourdomain.com; rua=mailto:aggregate@yourdomain.com;

Additionally, actively monitoring your sender reputation and checking for any blocklist listings is a continuous effort. Services like Suped's blocklist checker can help you stay on top of any issues. Swift remediation of any listings is crucial to prevent long-term damage to your deliverability.

Views from the trenches

Best practices

Actively manage your sending infrastructure and ensure all email authentication standards are correctly implemented for your domains.

Monitor email deliverability regularly to major UK providers and analyze engagement metrics to adjust your sending strategies.

Segment your email lists to ensure you send relevant content to engaged subscribers, reducing spam complaints.

Common pitfalls

Overlooking smaller, regional UK ISPs and mailbox providers, as they can still represent significant audience segments.

Not removing unengaged or invalid email addresses, which can lead to higher bounce rates and spam trap hits.

Ignoring DMARC reports, which contain critical data on email authentication failures and potential abuse of your domain.

Expert tips

Keep an eye on trends in email filtering within the UK, as local mailbox providers may adapt their policies faster to regional spam patterns.

Investigate any sudden drops in deliverability to specific UK providers, as it could indicate a new blocklist listing or policy change.

Develop relationships with postmaster teams where possible, especially for larger mail streams, to resolve complex deliverability issues.

Expert view

Expert from Email Geeks says that data on top UK mailbox providers can be skewed depending on how it's collected, for example, by focusing only on .uk domains, which might underrepresent actual ISP mailboxes and filtering services like Proofpoint or Cloudmark.

2022-12-05 - Email Geeks

Marketer view

Marketer from Email Geeks says that some services appearing on lists of top providers might be better described as filter providers, rather than direct mailbox providers, which is an important distinction for deliverability.

2022-12-05 - Email Geeks

Keeping your emails landing in UK inboxes

The UK email landscape, like many others, is dominated by a mix of global tech giants and strong local players in both the ISP and mailbox provider sectors. For anyone sending emails, understanding who these key players are and how they operate is fundamental to achieving high deliverability rates.

Focusing on strong sender reputation, proper email authentication, and continuous monitoring will help ensure your messages consistently reach the inboxes of UK recipients, regardless of their chosen provider. Effective email deliverability is a continuous process of adaptation and optimization.