What is what? Bounces, complaints and blacklists

Bounces are any email that’s been rejected by your recipient’s mail provider and
was sent back to you. Complaints are (inherently!) self-explanatory. Both can get you blacklisted by email service providers. Let’s look at the connection between bounces, complaints, and blacklists in more detail below.

Hard bounces

A hard bounce indicates a permanent reason an email cannot be delivered. Some common reasons an email could hard bounce are:

  1. The recipient’s email address doesn’t exist.
  2. The recipient’s email server has completely blocked delivery.

A high number of hard bounces can lead to your campaigns being blacklisted (if they aren’t already), because frequent bounces indicate you’re not maintaining list hygiene by removing bad email addresses.

You can easily prevent hard bounces by having a double opt-in process in place, letting go of old and unresponsive data, and suppressing hard bounces as they occur. If you aren’t sure about the validity of your data, you can use list hygiene software like EmailListVerify or NeverBounce to clean out hard bounces before attempting to send to older emails on your list.

Soft bounces

Soft bounces typically indicate a temporary delivery issue. While there are many reasons an email address may soft bounce, these are a few reasons this typically happens:

  • The mailbox is full (over quota)
  • The mailbox is not configured correctly
  • The mailbox is inactive
  • Recipient’s email server is down or offline
  • Recipient’s email server has been sent too many emails during a period of time
  • Your email message does not meet the recipient server’s anti-spam requirements


Spam complaints

Your subscribers can mark your email as spam by clicking on the “report as spam” button in their mailboxes. And too many spam complaints lead to your e-mails getting filtered or blocked.

In most cases, high complaint rates suggest poor email practices that over time lead to decreasing open and click- through rates, lower deliverability, and even permanent blacklisting by email service providers.

There are multiple ways you can reduce complaints. For starters, always stay relevant to your subscribers and don’t message them too frequently (see the section “Your Subscribers’ Expectations”). Also, some users opt for the “fast route”
and click the spam button as a way to unsubscribe quickly instead of scrolling through an entire message to find that particular link. Because of this, consider including unsubscribe instructions at the top of your e-mails in addition to the footer.

Recommended thresholds

It’s recommended you keep bounces and complaints to a minimum. Above a certain percentage you can expect major issues across most ISPs. Stick to these general guidelines and you should be safe:

  • Soft bounces – roughly 10-20 emails for daily sends, no more than 2-3 for weekly or monthly emails
  • Hard bounces – varies, but 3-5% is accepable
  • Spam complaints – below 0,5



An email blacklist is a database that outlines certain criteria to determine if an IP or sending domain is being used to send spam. These lists are used and updated by ISPs to prevent spam messages from reaching peoples’ inboxes.

Being on a blacklist is every email marketer’s worst nightmare, so how do you know if you are currently listed?

If you have a feeling that your emails are not getting through as your open rates have plummeted, you can check your IP address or sending domain on either MultiRBL or MxToolbox to see if you are listed.

Some of the better-known blacklist operators include Spamhaus, Spamcop and SORbS.

It’s always better to act on blacklisting as soon as possible, so we advise you check this on a daily basis, if possible.
If you do find that you are listed, it’s not always the end of the world since it’s likely you are able to remove your IP address or sending domain.

You first need to discover the reasons as to why you’ve been blacklisted from the information provided by the blacklist operators, and then take your time to resolve these issues. You should find instructions on how to get yourself removed from them, so make sure to follow these guidelines to get back to delivering relevant content that your subscribers want to read.

It can be time-consuming to stay on top of your reputation and monitor your presence on blacklists, but rest assured our delivery experts at Inboxroad work to proactively delist you.

Feedback loops

Feedback loops are programs set up by individual email service providers to notify senders each time their emails are reported as spam.

If you register your IP or domain with these service providers’ feedback loops, you can avoid sending more campaigns to anyone who reported your content as spam. This will also help you better manage your reputation across these providers.

Inboxroad automatically signs you up for most ISPs’ feedback loops except Yahoo’s, which customers need to set up on their own.

ISP best practices

Everything you’ve read up until this point will help your emails get delivered with minimal problems across most email providers and ISPs. However, each ISP has its own rules for what does and doesn’t get delivered, which unfortunately aren’t always public knowledge. That being said, you can take a few proactive steps to make sure your emails are more likely to be delivered to inboxes.

Want a detailed overview of specific rules per ISP? Download our full guide to email deliverability in 2021.