There’s something about bounces

I’ve shared a version of this image repeatedly. I think it was only my Facebook friends that got the stick figure screaming in frustration, though.

An overlapping circles diagram showing bounce classifications from 3 different ESPs and how they overlap (and don't) with each other and with my classifications of the underlying error.

The reality is bounce handling is one of the most frustrating pieces of email delivery. Not only that, many people in the email space treat it as a simple process. It’s really not as simple as we’d like it to be.

The above image was created based on docs from 3 different ESPs a client was using. They wanted to normalise their bounce handling across ESPs, and asked me for policy recommendations. I ended up digging through a bunch of docs from their 3 ESPs. I recorded the reasons as reported in the docs in a colored block corresponding to the ESP, then dropped them in the appropriate circle: soft, block or hard.

The shaded circles are based on my interpretations of why these bounces happen.

  • The big grey circle surrounds bounces due to reputation issues.
  • The green circle is primarily networking and technical issues.
  • The top purple circle is non existent or bad addresses

Note, nothing here indicates how we should react to the bounces, this is just a categorisation activity. This classification also has nothing to do with what the actual SMTP response is.

Just remember, next time someone says bounce handling is simple: they’re wrong.

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I often get clients and potential clients asking me to tell them what the absolute best ESP is.
“You’re an expert in the field, which ESP will give me the best inbox delivery?”
The thing is, there isn’t an answer to that question.
ESPs have expertise in sending large amounts of mail.  All have staff that manage and monitor MTAs. Most have staff that provide advice on delivery issues. Many have staff that handle abuse complaints, FBLs and blocks.
What they don’t have is magic delivery fairies or bat phones into postmaster desks.
Simply moving mail to an ESP won’t give you delivery. For the most part, delivery is the responsibility of the sender, whether they send mail through an in house system or through an ESP.
Delivery is primarily about how recipients react to a particular mail stream. Send mail recipients want, interact with and relate to and you usually see good delivery. The IP addresses or infrastructure contribute but do not dominate the equation. Sending from an ESP won’t fix poor content, irrelevant mail or unengaged recipients.
I can hear everyone now shouting at their screen “What about shared IPs!!!?!?!” Yes, yes, if you use an ESP with shared IP addresses and the ESP gets a bad customer you may see poor delivery for a time because one of their other customers was bad. It’s a fact, it happens. Plus, if you use an ESP with dedicated IPs and the ESP gets a bad customer you may see poor delivery for a time because one of the other customers was bad and their IP is near yours.
So clearly the answer is to bring email in house. That way no other company can affect your delivery, right? Yes. Kinda.
Are you willing to invest money in hiring email and DNS savvy sysadmins? Invest money in a MTA designed to handle bulk mail? Invest in an expert who not only understands bounce handling, but can explain to your developers what a good bounce handling system must do? Invest in someone who can manage authentication like DKIM? Who can handle delivery issues and understands how to talk to ISPs? Invest in development to write a FBL processor?
For some companies, the internal investment is the right answer, and bringing mail in house makes business sense.
For a lot of companies, though, they just want to use email to communicate with customers. They don’t want to have to invest in multiple staff members (as it’s very rare to find a single person with all the various skill sets needed) to just send a weekly newsletter, or daily sales email. They need a tool that works, they don’t need to know how to sign up for a FBL, they don’t need to know how to handle bounces. They can outsource that work and focus on the communication value.
Finding the best ESP starts with finding out how you want to use email.
Question 1: What role does email play in my business?

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In the email delivery space there are a lot of numbers we talk about including bounce rates, complaint rates, acceptance rates and inbox delivery rates. These are all good numbers to tell us about a particular campaign or mailing list. Usually these metrics all track together. Low bounce rates and low complaint rates correlate with high delivery rates and high inbox placement.

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Relaying Denied

I’ve got multiple clients right now looking for insights about bounce handling. This means I’m doing a lot of thought work about bounces and what they mean and how they match up and how different ISPs manage delivery and how different ESPs manage delivery and how it all fits together. One thing I’ve been trying to do is contextualize bounces based on what the reason is.
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Relaying Denied means the mail server you’re talking to does not handle mail for the domain you’re sending to. 
Well, OK, but how does that happen?
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DNS records are incorrect. These can be due to a number of things

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