Deliverability Interviews – Radek Kaczyński from Bouncer

Interview with Radek Kaczynski from Bouncer

Interview 6: This is our sixth interview in the deliverability interview series. In this interview we spoke to Radek Kaczyński from Bouncer.

Radek is a believer in the possibility of improving Human to Human email communication. And thus since 2017 has been building Bouncer (email verification and deliverability start-up) to help people get and stay connected via email.

He does not consider himself an email deliverability expert, but while working on Bouncer has learned a few things about email and deliverability too 😉


If you missed our earlier published interviews in the deliverability interview series you can read them here.


Interview Date: May 10th, 2022

Postbox Services: Good Morning Radek. How are you?

Radek: Good morning Sandeep, I’m great! 

Actually… personally, I am having the best time of my life 🙂

Postbox Services:  That is really great to know 🙂

Radek, you are the founder and CEO of Bouncer. Could you tell us how you came up  with the idea of Bouncer and how has the journey been so far?

Radek: Our story is quite different from other email verification providers’. My background was neither in email nor marketing. During my whole so-called career, I’ve been in IT. First, I’ve been  building, maintaining, and enhancing IT systems. And later – managing portfolios of critical IT  solutions. While working for Volvo Group in the U.S., we had a challenge with the continuity of  the communication via email. When the truck was coming for the service, and the contact email  address was passed over the counter – there were plenty of typos. And not only was it causing  issues for communication for this particular service event, but also later down the road with the  surveying processes or ability to contact decision makers with some special offers, etc.

And when I was looking for a solution, I learned about email verification. But I noticed no  options that combined technological sophistication with ease of use. What I was looking for was:

  • high precision with bias against false negatives – so that people don’t lose the ability to  connect because of the wrong categorization,
  • high coverage – ability to verify email addresses hosted by different email service  providers (low amount of unknown results),
  • high performance – speed of verification and generous rate-limiting, 
  • security with no compromises – especially as data protection became more critical.

I decided to quit my corporate life, move back to Europe and start Bouncer. Should I have  known how hard it would be, probably I would not do it, and yet I’m so happy I didn’t know that  😉

It was pretty naive as I did not have any background in the email field and almost no  connections. Even more naive was thinking that we could build a Backend as a Service, API only solution and will be able to convince MarTech folks to embed our Email Verification  solution inside theirs.

But I felt that we would be able to build the most intelligent and yet easy-to-use email  verification solution with the right team.

And I had much luck in attracting such talents.

After a few months of hard work, we indeed had a great core of the system – we were so surprised to hear from experts and former employees of our competitors that Bouncer has the  highest coverage and best precision.

But just a great product does not guarantee “success”. We realized that our business is not  sustainable with an API-only approach, so we decided to diversify our customer base and serve  marketing teams directly; thus, we needed to create a super-easy-to-use Web App.

Simply put, sales cycles were too long when we were trying to convince MarTech solutions to  use our backend. We did convince the more progressive ones, but it was not enough to survive.

We still advocate that email verification should be embedded in marketers’ solutions. It’s perfect  when there’s no need to switch, learn, and spend time/energy/talent on email verification.

But if your tool of choice does not have email verification inside – you can use Bouncer’s email  verification app to clean your list in a few steps. And then, you can recommend your Email  Service Provider to integrate with us and have Bouncer inside 😉

Postbox Services: Could you tell our readers the importance of email list cleaning. Do you recommend  cleaning only old lists or even the lists which are continuously being emailed?

Radek: Having your email list clean is one of the more essential aspects of deliverability. Email service  providers, while fighting spammers, use bounce rate as an indicator of suspicious behavior. And  good people are getting a ricochet as well.

Studies show that if 20% of your emails bounce, there is a very high probability that you will be  listed on blocklists, and your deliverability may drop by 50%. When you are listed on blocklists,  email service providers may block your messages, regardless of whether the recipient address  exists. Many email service providers will warn you when your bounce rate is over 5% and may  suspend your account when it’s higher than 10%. They do it to protect both your sender’s  reputation and their infrastructure.

The process of getting delisted usually is not super-difficult, but it takes time and prevents you  from having your communication going.

Add to that the fact that up to 15% of business email addresses get obsolete in just one year – primarily because of personnel rotation. Plus, 5-10% of email addresses are incorrect at the  moment of entry (especially when spelled over a phone or counter or typed on a mobile device).

That’s why email verification is so helpful – letting you clean your email list and spot the typo in  real-time.

If it comes to the frequency of the list cleaning…

Suppose you are sending emails to your recipients on a regular basis, and you do manage all the  bounces and auto-responders. In that case, you don’t have to use email verification very often  because you are handling it in a healthy way.

But if you are engaging with your audience less often than once a month – it might be valuable to  clean your list before each bigger send-out. Iza from our team has written an excellent article on  how often you should clean your email list 😉

Postbox Services: When we clean the lists using Bouncer, it also tells us the domain of the email address  and the provider of the email address. Could you talk about how these two columns can  help email marketers? Let’s say the provider of an email is Proofpoint or Outlook. How do  marketers need to change the approach on the basis of the provider?

Radek: These data points indeed are pretty powerful for more experienced users – they inform you which  email service provider is being used by your recipient. This information can help both proactively and retroactively.

First of all, after verifying your list, we advise you to import the provider field to your CRM /  marketing automation or any other MarTech tool. Then when you are getting some bounces, you  will already have visibility what’s the email service provider, and maybe there is some correlation between a higher amount of bounces and a provider. This helps to spot the  deliverability issues for specific providers.

Additionally, when you have some challenges with a particular provider, you can segment your list and adequately manage the flow and volumes of emails.

For example, you might want to  slow down sending out to Proofpoint if you had some deliverability issues with them before. Or  you may want to be a bit more cautious with sending to catch_all emails hosted by Outlook. 

The majority of the senders don’t need to bother about that. However, it helps in cooperation  with deliverability experts like yourself. It is also essential when performing root cause analysis  and disaster recovery after deliverability problems.

Radek: We are thrilled that finally, we can provide our customers the information about the toxic email addresses that might have resided in their email lists.

Radek Kaczyński

Postbox Services: Bouncer has recently launched Toxicity Check (Blackbox). This seems to be a very  interesting and important feature. Could you tell our readers about it? Is it not safe to send  an email if the toxicity level is anything above “0”?

Radek: We are thrilled that finally, we can provide our customers the information about the toxic email addresses that might have resided in their email lists. And by toxic email addresses, I mean: 

  • Widely circulated ones – those included in the databases that are being frequently sold.  When you are sending to such email addresses, there may be a risk that someone will think you are one of the spammers that purchased their email address.
  • Breached email addresses – for which the email account has been hacked. This may mean that a person behind the email address is using a stolen email address and trying to  impersonate the original owner.
  • Complainers – email addresses of people who do “report as spam” when they get  unsolicited emails.
  • Litigators – email addresses of known privacy and security litigators.
  • Potential Spam Traps.

As with everything related to deliverability, whether you should send to recipients with a toxicity score higher than 0 depends on a few factors. It mostly depends on how well you know your  audience and how you have been engaged with them.

If the email addresses are of people you’ve been interacting with and have a relationship with,  you should still be safe. Maybe a litigator or a complainer on your list is an email geek fighting for the secure email ecosystem? Or perhaps they have self-registered as a spam trap, so they  don’t get unsolicited emails? Or maybe they do report spam but will not do that for your  messages because they know and like you.

But if you haven’t been in touch with them for a long time, or even ever, I recommend being cautious.

Postbox Services:  I saw a great article on Spamhaus published by Bouncer. From your experience does Spamhaus only blacklist a domain or IP when a real email is sent to a spam trap, or can it  blacklist even if we just check the validity of the email address by opening an SMTP  connection?

Radek: Ohh, thank you! Yes, Iza writes great articles 😉

Even an SMTP check can cause a block on Spamhaus, if I’m not mistaken. That’s why we also  have to take care of Bouncer’s infrastructure. Ultimately, our business is taking a risk from our  customers on us and managing it properly.

We earlier published an article by Iza on The importance of email verification

Postbox Services

Postbox Services: In the last week of February we saw some spam filtration changes implemented by Yahoo which affected many email marketers. Do you have some insights on this and what  are your deliverability recommendations?

Radek: Like other Internet Service Providers, Yahoo is changing its spam filtration rules from time to  time – to adapt to the current circumstances. As I mentioned before, there has been a fight  between Internet providers and spammers going on for a long time. And decent marketers get a  hit as well, from time to time too.

I have heard that there were some deliverability issues back in February and March, especially  for mainly senders from the political and insurance industries. What I think might have happened  was that Yahoo (their postmasters or artificial intelligence) noticed many spam messages with  political and insurance-related content.

And their anti-spam rules have been changed, resulting in some legit senders being affected,  unfortunately.

Of course, Yahoo couldn’t point out the details and reasons why some messages were bouncing  because they didn’t want to give the clues to the spammers.

That kind of situation happens and will be happening in the future, so it’s good to observe if, for  example, Yahoo has changed its best practices, and if there is no clue – contact their postmaster.

Email Experts like you are beneficial when such situations occur, so we should not be afraid of  contacting one 😉

Also, the Email Geeks community is super helpful and may shed some additional light if  something is weird – In March, I saw many valuable insights about this issue.

Postbox Services: These insights are quite helpful for our readers. Thanks.

How is your newly born  daughter doing?

Radek: Thank you very much, Sandeep – for your kind words and allowing me to share. It’s been a pure  pleasure talking to you again, and I must say – I loved your questions! 

Ohh… she is a blessing. Actually, becoming a father is the reason why I’m having the time of my  life right now.

We all are still learning a lot about each other – it’s new to all of us – it’s our first baby, and it’s a  lot of first times for our baby-daughter Lena too 😉

Postbox Services: Thanks Radek. We have personally been using Bouncer for quite some time now and have been recommending it to our clients all along. We simply love the Bouncer. Great to see all the progress Bouncer is making as a tool. All the best to you and the team.


If you need any help with/consultancy related to email marketing, email deliverability or email infrastructure please reach out to us.