Everything You Always Wanted to Know About Email Bounces

Massimiliano Chiucchiu

If you are in charge of creating and managing email campaigns, you’re probably dealing with emotions that only mass emailing can give you. Once you hit that “Send Campaign” button and get rid of the excess adrenaline with a nice shower or a liberating cry in the bathroom stall, it’s time to go back to the front lines. At this point in the game, it really gets tough: it’s time for analysis!

Put on your lab goggles and get ready to handle the results of your recent massive send out. A mix of registrations, purchases, compliments, but also (and above all) complaints, cancellations, and a lot of messages from a certain Mr. Daemon. Mailer Daemon.

Welcome to the world of bounce!

Why Does an Email Bounce Back?

Don’t panic. Or maybe you do panic… Because every bounce received is a notification that informs you that, for a certain reason, your message could not reach the recipient and this impacts your domain and your IP reputation.

Bounces are divided into Soft Bounces and Hard Bounces— a bit like porn (I’m sure I could have used a more professional metaphor, but I’m just as sure that, at least for a few seconds, I had your undivided attention).

1. Soft Bounces

The soft bounce refers to messages that are not delivered due to:

Your recipient’s mailbox is like a club that doesn’t let you in because you don’t match the required dress code. The security staff wants to maintain a certain type of quality and it seems that you are not, at that time, up to it. Soft bounces refer to a temporary problem. They are easily recognizable because the error message is often preceded by a three-digit number starting with 4.

But why does this happen? If your sending domain or IP reputation is low, it can be attributed to the major ISPs (Gmail, Yahoo, Microsoft, etc.). It is likely that your previous campaigns or even the one you just sent have generated a high rate of complaints (users who click on the “report as spam” button). This is considered the most important indicator for ISPs to choose which infernal round to place you in. They also consider many other parameters, including the number of spam traps hit or messages ignored.

How To Heal Your List From Soft Bounces

If the error text you get refers to messages rejected by the recipient server, then we have a reputation problem to fix. Usually, it is enough to send emails to loyal recipients (which you should always do anyway) who habitually interact with your messages, like opening the emails and clicking on available links. This is because ISPs tend to reward senders who take care of their mailing lists, scrubbing them clean from users who no longer show interest in those communications. List cleaning is also recommended in the case of “mailbox full” errors.

If the bounce is due to a technical problem of the recipient server, it is usually enough to wait a few hours and send the message again.

Note: For ISPs, sending mass emails with attachments (especially heavier than 1MB) is a big no-no. It puts a lot of strain on your SMTP server and the recipient’s mail server to download it. As a result, ISPs are a bit allergic to this practice and will reject the message.

Now that you know how to bounce back (pun intended) from soft bounces, let’s take a look at hard bounces.

2. Hard Bounces

Unlike soft bounces, hard bounces are permanent non-delivery notifications and always relate to the unavailability of the recipient’s mailbox. Just like when you break up with your girlfriend/boyfriend and start messaging your old friends again, but in the meantime, they’ve changed their phone number. Friendships must be nurtured. Similarly, if you don’t keep your mailing list clean or up to date, you risk finding yourself without recipients.

But hard bounces can also be the result of an inaccurate transcription from a paper form collected in-store or a clumsy user who did not write his email address correctly during registration (and your registration procedure does not include double opt-in).

How To Heal Your List From Hard Bounces

If you see an error message with a three-digit number starting with 5, there is only one solution: delete the related email address from your list. Hard bounces will damage your reputation with ISPs and could negatively affect your next send out in terms of performance and inbox rate. So it’s better to part ways with the email address, rather than to hold onto it “just in case.”

Wrap Up

In short, handle your list the way you would like other bulk mailers to handle your email address. A little humility doesn’t hurt. You can’t expect everyone to be interested in your messages. So let go and stop sending to uninterested users and focus on keeping new and active ones. If you do, you’ll hardly see bounces in your next campaign stats.

Soft or hard, it doesn’t matter… Your bounces will never go unnoticed. ISPs already know who you are, where you send from, when you do it, what you send, who your recipients are and how they behave with your emails – whether you like it or not 😉

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