The last thing any email marketer wants is to see emails returned when a campaign is on its way out—nudging up their bounce rates. Whether they’re labelled with message failed, rejected, or bounced, it all adds up to the same thing—they’re not hitting their intended inboxes. Do you know why your emails are coming back as undeliverable?

There are 2 main types of an undeliverable email

There are two types of email bounce: soft and hard. One garners more concern than the other, but if either is appearing in your email campaign lists in higher numbers than acceptable, it’s time to find out why.

1. Soft bounce email returns

A soft bounce is a temporary problem. Your server will keep trying to deliver your email until it finds its way into its intended inbox, or it gives up after a set number of attempts or time limit.

Soft bounces can be caused by temporary disruptions to the server, the recipient’s mailbox being full with not enough server space for your message, or your email content was simply too big.

Don’t delete soft bounce addresses prematurely—they often resolve themselves without any action. However, persistent soft bounces need investigation, and if you can’t sort the issue, you need to consider removing them from your lists.

2. Hard bounce email returns

A hard bounce is a little more serious as it announces a permanent problem. Permanent rejection means that the email address doesn’t exist, it doesn’t have the email server it needs, or that the address is invalid for some other reason. It could also mean your address is blacklisted or banned by the recipient server.

Hard bounced emails need removing from your lists if it isn’t possible to find the error and fix it.

Types of undeliverable emails

The following list includes most of the common reasons for your bounced emails. When emails are returned, for whatever reason, they typically include an automated explanation of the problem. Each issue has a specific code, giving a brief explanation of the problem in that instance.

1. Non-existent email addresses

There are many reasons why a once active and healthy email address can disappear. Employees leave jobs and organizations, they update domain names when re-branding or change service providers, and with that, their old contact details cease to exist, including their email addresses.

2. Email address errors

A common problem for email marketers is human error. It’s so easy to mistype an email address, even when users know them off by heart. Alternatively, if you’re sent an email in a handwritten format, they can be pretty hard to decipher at the best of times.

3. The server is unavailable

If your mail server can’t find the recipient’s mail server, then it has no chance of delivering your email—it would be like trying to post a letter to a house that doesn’t exist or is on an unknown street!
Servers can go offline for all kinds of reasons: it could be because of scheduled maintenance, being overloaded, it may have crashed, or from some other complication with server space or function. Typically, these errors deliver soft bounces, so keep an eye on them if they persist; there could be a more serious issue afoot.

4. Mailbox full

Poor email management leads to overflowing folders and full mailboxes. Where a mailbox exceeds its limit, and there’s no space for your message, it’s returned as a soft bounce. It could be that the user is disorganized, but it could just as easily be that they’re no longer using that account.

5. Your email message exceeds the recipient’s limits

Depending on how each recipient sets up their email account, the typical limit for email size is somewhere around 10Mb. If your messages contain large files, or if the recipient has set far lower limits than what’s usually accepted, the server will reject it due to being too large.

6. You’ve gone over your sending limit

Some servers don’t permit sending emails in batches of more than 25 at a time. If you exceed the limit, then you’ll have problems—if you try to send batches of over 100, you might even get locked out of your own servers.

7. Blocked email addresses and denied permission

If your email address is blocked, it’s because the recipient’s server has decided it’s not trustworthy or the user has written specific rules to prevent certain types of messages from getting through.

Some servers are stricter than others: those of hospitals, surgeries, schools, colleges, and government offices, for example. If you experience problems with this type of recipient, you’ll have to contact them by an alternative means and have them add you to their ‘safe senders’ list.

Your email address may have received a bad reputation if it’s been used by spammers to deliver an underhanded campaign. Where that’s the case, you need to check industry blacklists to see if you’ve been marked as a spam sender. If so, there are specific steps to follow to clear your address.

8. Your emails are greylisted

If the incoming server doesn’t recognize the email’s IP address, it may temporarily reject it.

9. Auto-response messages

Although it’s not a typical bounce message as such, these replies will land in your inbox alongside your other error messages. When a user goes on holiday or isn’t in a position to receive and read their email, they set up automatic responses to let senders know that that’s the cases.

In these situations, the original email lands just as required in the inbox—the return message is purely for the sender’s information.

Are undeliverable emails bad for your deliverability?

If your bounce rates are steadily increasing, that’s bad news for your email sender score, and a poor sender score will ultimately lead to more and more messages failing to reach their target.
You’ll never wipe out email bounces completely, but you can keep them within safe ranges.

How to solve the issue of undeliverable emails?

To prevent your marketing teams from asking, ‘Why are emails coming back as undeliverable?’ then the following tips will help keep matters in check.

1. Clean your email lists

For the best email list hygiene, you should clean them regularly, preventing unnecessary bounces affecting your sender score. Whether you do that manually or with a list cleaning service or software, it should already be part of your marketing schedule. Software like ours helps to narrow down all kinds of problem email addresses and removes them with the click of a mouse.

2. Use opt-in methods for clean addresses

To avoid mistyped or fake email addresses being added through your sign-up forms, double opt-in methods ensure each added address is valid at the time of application.

3. Format your messages to be spam-proof

This isn’t one of the most typical technical issues, but if you’re not running your campaign messages through a spam checker, you’re missing a trick. There are countless phrases, terms, techniques, practices, and actions that servers see as potential spam messages. Formatting your messages to look like healthy, trustworthy messages requires a little careful thought and application.

4. Follow a regular schedule

Mail servers monitor how many emails you send and when you send them. They’re looking for the kind of erratic schedules that spammers use. If you want to avoid raising warning flags, build your email list numbers steadily and send out your campaigns on a regular schedule. You’ll appear as genuine as they expect you to be and judge you with a clean bill of health.

How Bouncer helps you keep your lists free from undeliverable email addresses

Your best friend to keep bounce rates down is an email list cleaner. Bouncer is a leading industry solution that helps marketers monitor and manage their lists, keeping them in optimum condition, with more of your emails landing in their recipients’ inboxes than ever.

Your messages must land successfully if they’re going to be read, returning the conversions you need. And for that, you need clean and healthy lists for all of your campaigns.