With email use worldwide set to top three billion users by 2020, it’s no surprise that businesses are recognising the value of email marketing. 

However, in order for email marketers to hit the deliverability sweet spot with customers, a certain degree of attention must be paid to mailbox providers (MBPs). Like any online trend, MBP usage varies globally and regionally, and with all MBPs stipulating different rules for deliverability, it’s vital that marketers understand the variations in criteria and tailor their email programmes to fit each MBP’s requirements accordingly.

Research shows that Outlook.com (and its corresponding Hotmail, MSN and Live) addresses dominate email marketers’ distribution lists in the UK, comprising between 35-40% of their recipients. Gmail and Yahoo run neck and neck for second place, with Gmail at about 13% and Yahoo at approximately 12.5%. Gmail is also showing huge growth in the millennial and Generation Z demographic, with close to 70% of younger people choosing this mailbox provider. Finally, BT comes in at fourth place, followed by Names.co.uk, TalkTalk, Virgin and BskyB, all of which have approximately the same number of registered email accounts.

MBP filter technologies and how to work around them

A key element of MBP criteria relates to spam filtering. While it would be ideal if there was a single algorithm that all of the mailbox providers use, there isn’t, which means Gmail, Outlook.com, and Yahoo! Mail all have their own unique spam filtering rules and services to help senders. MBP filters make decisions based on subscriber engagement, with each mailbox having different actions that could indicate low engagement levels, and subsequently files the email as spam. For example, Yahoo puts a heavy emphasis on URL filtering and complaints from users, while Outlook.com uses a SmartScreen anti-spam filtering technology that classifies messages based on email content and sender reputation.

To judge the success of an email programme and ensure that marketing emails are not being filtered into spam by specific MBPs, marketers need visibility so that they can differentiate between inbox and spam placement. There are also reputation measurement tools available, such as senderscore.com which indicates the health of an email programme and sender reputation. Having this actionable insight is a key step in nipping any reputation issues in the bud. 

List hygiene due diligence

MBPs also monitor email address lists. Sending just one marketing email to an invalid email address can cause havoc with spam rates, with a single Spamhaus listing having the potential to instantly halve programme performance. If marketers send to a large number of invalid email addresses and experience high bounce and spam trap rates, they may be stopped from reaching anyone on their lists. Indeed, if MBPs spot that a programme is generating a high number of bounce-backs, messages could be filtered or blocked altogether.

It’s therefore wise for marketers to have a strategy in place that guarantees only legitimate email addresses are added to the list in the first place. This can be achieved through using double opt-in, testing email addresses for structure (setting up a rule that only qualifies an email address if it has an @ sign in, for example) or real-time validation. Fundamentally, marketers need to think about how they can encourage new subscribers to provide a primary, live email address that will be much more responsive, therefore averse to being spam listed.

The legalities of email programmes

There are also legal requirements to consider when sending marketing emails. The EU Directive on Privacy and Electronic Communications Regulations states that senders cannot contact users without their prior consent unless they’ve obtained the user’s email address in the course of a business transaction. MBPs are committed to keeping their emails relevant and secure for their users, so it is sensible for email marketers to only use email lists from a third party if the recipients have expressly consented to receive messages from third parties. Indeed, this will be a legal requirement in the advent of GDPR, which is due to be enforced next year and imposes a greater duty of care on marketers to ensure that consent is explicit, transparent and evident. 

Marketers often think that it’s possible to avoid spam filters altogether, however it comes down to how MBPs perceive sender behaviour. With list hygiene, content, reputation and legalities impacting the way MBPs filter email, it’s integral for marketers to learn how each MBP’s filter technologies work and have full insight into their email programme to avoid any unnecessary spam placements. If marketers are alert and monitor the performance of their email programmes to ensure there is consistent subscriber engagement, they will enjoy the benefits of strong relationships with each and every mailbox provider.