Email deliverability is the rate at which your emails reach an inbox. Optimising email deliverability is the foundation of an effective email marketing strategy. The greater the number of your emails that reach their intended destination, the greater the likelihood of opens, clicks and conversions.

Meanwhile, sending a lot of emails to the wrong places - such as dormant or non-existent emails - can give you a reputation as a spammer, leading mail servers and spam blockers to take a dim view of your campaigns in future.

As such, it's essential that marketers take steps to ensure their email deliverability rate is as high as possible. One of the simplest ways to do this is using an email verifier service to check whether the email addresses on your list are valid.

Remember: the validity of your email data could change at any time, such as when one of your contacts leaves their job and their inbox is shuttered. As such, it's a good idea to run your list through a list checker on a regular basis.

A "bounce" is what happens when an email fails to reach the intended inbox. This normally means the email has been rejected by the mail server.

There are two types of bounces: hard bounces and soft bounces. A hard bounce means the failure is permanent: the email address or domain may not exist, for example, or the mail server may be set up to reject incoming email. A soft bounce, meanwhile, is more likely to be a fixable issue: it may indicate that the recipient's inbox is full, or there's a temporary issue with the mail server.

Bounces are bad for business in a number of ways. Firstly, for obvious reasons, a high number of bounces will detract from the success of your campaign because it means many of your emails are failing to reach their intended recipient. (It can also lead to an inbox clogged up with non-delivery reports, which take time and effort to deal with.) Secondly, sending a lot of emails that bounce can make you look like a spammer and cause lasting damage to your reputation as an email sender (more on this later).

Using an email verification service offers a simple and painless way to remove confirmed and possible bounces from your email list, protecting your business from high bounce rates, non-delivery reports and a damaged sender reputation.

Whether they know it or not, every business that sends emails has a "sender reputation".

This is a complex metric used by mail servers, internet service providers and anti-spam solutions to determine whether your emails should be delivered to the intended recipient, sent to their junk or spam folder, or blocked outright.

Sender reputation isn't based on any one factor - it's more like a credit score that represents your overall reputation as a sender. You can't see it, but it affects every single email your business sends - and, also like a credit score, it can be built up or damaged over time depending on how you act.

Some of the factors that can affect sender reputation include the deliverability of your emails (a lot of bounces are likely to hurt your reputation), the level of engagement your emails see (do the recipients open them?) and whether they are ever reported as junk or spam.

Your sender reputation is associated with both the IP address and domain of your outbound emails. This means that if your sender reputation is ever damaged, that damage can last as long as you continue to use the same mail server or business domain. It's not easy to wipe the slate clean.

However, you can build up your sender reputation over time (and recover from damage to your sender reputation) by ensuring that your emails are delivered successfully, engaging to your audience, and not mistaken for spam. Using an email validation service will help you improve the baseline by flagging dormant and non-existent emails.

For companies that provide apps and online services, sign-up forms can become a common and prolific source of bad email data.

While most customers should be willing to sign up for an app or online service using their correct email address, others will enter fake credentials or set up a disposable email address as a way to hide their identity. Reasons could include:

• Taking advantage of a free trial or special offer multiple times
• Taking advantage of free content (such as ebooks) offered in exchange for an email address
• Intent to commit fraud using stolen credentials

It can be very difficult for companies to identify users that fit this profile - and, by the time they do, the damage may have already been done.

However, API-based email verification offers one possible solution. Because malicious users often use fake, temporary or compromised email addresses, checking their email address for red flags at the point of sign up can be an effective way to stop them at the border.

When you verify an email address, you’ll see one of three main results: OK, Bad, or Unverifiable. Each reflects how safe it is to send to that address, based on what our Hippo email checker found during the verification process.

OK - The email address exists and is safe to send.
Possible reasons for an OK result:

• OK / Success – The mailbox is active and accepting mail.

Bad - The address cannot receive email. Sending to it will harm your deliverability.
Possible reasons for a Bad result:

• Domain is inexistent – The domain doesn’t exist, so the address can’t receive mail.
• Mailbox full – The inbox exists but cannot accept any more messages. Normally a sign of an abandoned mailbox.
• Mail server fault detected – The server is misconfigured or experiencing issues.
• No MX servers found – No mail exchange servers exist for the domain, so delivery isn’t possible.
• Possible spam trap detected – The address is highly likely to be a spam trap. Do not send.
• Server does not support international mailboxes – The server can’t handle international characters in the address.
• Too many @ signs found – The address is incorrectly formatted and invalid.

Unverifiable - We couldn’t confirm whether the address is valid. These results may be temporary, and some addresses can still receive mail. Possible reasons for an Unverifiable result:

• Domain is well-known DEA – The address belongs to a disposable email provider.
• Greylisting – The server asked us to try again later as part of its security checks.
• None – The server didn’t provide enough information for a conclusion.
• Server is catch-all – The domain accepts all incoming mail but doesn’t confirm individual mailboxes.
• Unpredictable system – The server responded inconsistently or behaved unusually.
• Unknown – No additional information could be retrieved beyond the primary result.