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Deliverability 101: Explaining bounces

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Hi there,
I often hear from people wanting to know more about the mysterious world of deliverability. It’s a really wide topic, affecting almost all technical areas of newsletter creation, but I thought a good place to jump in would be bounces.
You’ve probably heard the term — it essentially means an email hasn’t reached a subscriber. Here, I’m going to drill down on the different types of bounces you might encounter, what they mean for your sending, and how you can best avoid them in the future.
Fasten your seatbelts.
Let’s start with a quick definition. Deliverability is a term that encompasses everything to do with the successful delivery of an email to your subscribers’ inboxes. It can be affected by lots of different factors. Some are technical, others are less technical.
When an email isn’t delivered for any reason — and there can be a lot of reasons — that’s called a ‘bounce’.
Types of bounces
While there are many reasons for an email to bounce, they generally fall into two wider categories: soft bounces and hard bounces.
Soft bounces
Theses are temporary blocks that should eventually resolve, and aren’t a reason to remove an email address from your subscriber list. If an email soft-bounces, it means the email address is valid and the email reached the recipient server, but it bounced back. Common reasons include:
  • The mailbox was full
  • The recipient server was down
  • The message exceeded the size limit allowed by the recipient inbox
  • One of your email service provider’s sending IPs is temporarily on a block list (more on this later)
Most email service providers will attempt to re-send an email up to a certain time limit, say 72 hours. After that, they won’t try again for this particular email, but will try to send to the address in the future.
Hard bounces
These are permanent rejections, and generally unresolvable. At Revue, we remove email addresses that have hard-bounced from your email list. Common reasons include:
  • The email address doesn’t exist (People sometimes give a fake email address when asked for it in return for content — this can be avoided by using a double opt-in, like we do when someone signs up for your Revue newsletter)
  • The email address is invalid (It might have a typo, not be in the correct format, or be out of use. This can happen when someone gets a new email address)
We remove these email addresses from your list because if the hard bounces mount up, that can damage the reputation of your newsletter, and of the IP we send your emails with — which can cause more emails to be sent to the spam folder or blocked by spam filters entirely. This would affect your deliverability, but also that of other people who use the same sending IP.
Talk to me more about block lists and IPs
Bear with me, this gets a bit technical.
When you use Revue to create and send newsletters, your emails are sent from our servers. We have a few different sending IPs — addresses that pinpoint the sending server for emails — and they are shared with other people who use Revue.
When enough emails sent from an IP address bounce, that can damage the sending reputation of that particular IP. This is especially likely to happen when people import large subscriber lists from elsewhere into Revue. Here’s why:
  • Sometimes those lists are years old, and many emails on it are now invalid
  • Sometimes the lists might have been bought or obtained without gathering consent from the subscribers via a double opt-in
We are constantly working to ensure imported lists live up to the same standard as lists built on Revue via our double opt-in system.
When large numbers of bounces are recorded in a short period of time, either by accident or due to the actions of spammers or other bad actors, our IP address may be listed temporarily on a block list, which means some emails won’t be delivered. When we become aware of this, we jump into action to get ourselves de-listed (this often means removing specific spammers from the platform, and building any technical barriers required to stop them coming back).
What you can do to prevent bounces
There are some types of bounce that you can’t influence — they’re just part and parcel of sending email newsletters. But there are some key rules you can follow to give your emails the best chance of landing in the inbox:
  • Use double opt-ins: This is the holy grail, and it’s best-practice for sending email newsletters. A double opt-in is when someone enters their email address into your subscription form, then receives an email to that address which they’ll need to click through to confirm their subscription. This happens automatically when people subscribe to a Revue newsletter. It results in a more engaged subscriber list, and weeds out invalid emails.
  • Check your list health regularly: Just because somebody once signed up with a valid email address, doesn’t mean that email address will stay valid forever. Export your subscriber list and run it through a tool like Neverbounce. That will give you an estimated bounce rate for your list — anything above 3% is cause for concern, and should be ‘cleaned’ (a process which removes invalid email addresses).
  • Make sure your emails don’t look like spam: This is a tricky one, because there’s no all-encompassing list of words or phrases to avoid (if there were, spammers would find ways to avoid spam filters entirely!). In general, avoid too much punctuation (??!!) in your subject lines and avoid using phrases linked to financial promises.
  • Ask your subscribers for help: Ask them to mark your emails as important/priority/VIP. Ask them to add your address as a safe sender to their contacts. If you’re building a community around your work and you have an engaged contact list, people should be happy to help you out. Why not ask them to do this from the get-go in your welcome email?
Phew. Lots of information there. And we didn’t even go into all of the technical details (which you’ll no doubt be grateful for!). If you have further questions about this you can reach us at — always happy to help.
For now, let’s take a look at what’s been going on in the newsletter world this week.
The week in newsletters
Here’s the September edition of Not a Newsletter, by Dan Oshinsky
What I learned from a year on Substack - by Casey Newton
WaPo and Social Spider use email to showcase the best - not just the latest - news stories
How Axios is tackling local news: newsletters from small teams, in more markets
That’s all from me today, I hope you have a great week, and see you next time!
Best wishes,
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Anna from Twitter
Anna from Twitter @revue

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