we’ve all been there: a message you sent to your users or customers ends up deep in a gmail spam folder, and it’s up to these people to “report as spam” and move it to the inbox. entry. if they are super nice, they send you an email to let you know about it.
but what do you do if gmail completely rejects your message and blocks it on the first connection to gmail servers, even before it reaches anyone (including spam folder)? that could be due to an error like this:
This smtp error tells us that google blocked the mail due to low domain reputation. but what does that mean? researching this specific error is…complicated. trying to search for it in the google guides will return very basic results, and even the gmail how-to guides are suspiciously light on the “low reputation” issue:
Rebuilding reputation after this kind of bounce is hard, as affected recipients won’t have the option to correct Gmail by moving the message to their inboxes. And because Gmail is such an important inbox provider, you really don’t want this to happen to you. So let’s see what we can do about it!
what is a gmail reputation based bounce? #
a gmail reputation bounce occurs whenever the system treats a message as suspicious for reputation-related reasons; for example, because the sending domain has a low reputation, the message links to someone with a low reputation, or matches recent spam trends. detected by gmail filters. reputation bounces can appear as 4xx or soft bounce (as in the example above), where messages are temporarily blocked until the sender can improve things, and as 5xx or hard bounce (as in the example below), where gmail is really trying to draw your attention to the fact that there is a serious deliverability issue.
Step 1: Identifying the problem and assessing damage #
Because it’s so rare and elusive, this bounce should immediately raise some serious red flags.
the problem is that a reputation-based bounce problem is hard to detect. google’s own postmaster tools allow you to analyze email performance and analyze delivery errors and spam reports, so if you’re using it (and we recommend you do), you should be able to see when something isn’t right. ok…
…but the tool may not actually address the reputation issue specifically: you will need to do extra digging on your own if and when you see a dip in performance trends. Plus, Postmaster Tools only works well if you send enough email to Gmail to anonymize the data; otherwise, you may see empty charts.
as an alternative, postmark is one of the few email service providers (esps) that will actually make reputation related gmail bounces, and all other types of bounce errors, visible to you as sender. while other providers will only alert you to a soft or hard bounce, the postmark shows the full bounce response, response headers, and more detailed classifications such as “isp block”, so customers can use this information to measure performance and gmail deliverability more directly.
step 2: optimize your participation #
some may speculate that a change to the content here or there would solve the problem, but then remember that google’s approach to filtering and displaying content is possibly the most advanced in the world, learning from mistakes and trends in real time . beyond that, it prides itself on catering to the individual experience, tailoring its filtering processes to match a single user’s preferences.
that means in addition to monitoring bounces, you want to keep a close eye on engagement metrics:
- if a low percentage of people open and click, gmail may start to think these messages are not that important
- if some people also mark messages as spam, gmail will see them as unsolicited
This combination of low open/click rates and high abuse reports affects the domain’s reputation as a sender.
Pro Tip: Just as this negative interaction can ruin a sender’s reputation, positive interaction over time can build it back up again. Use your transactional mail and other high-engagement streams to target your most active contacts, increasing your overall engagement rate and empowering spam filters like those at Gmail to more fully trust your messages.
Always keep a close eye on engagement metrics. if a low percentage of people open and click, gmail may start to think these messages are not that important.
step 3: protect your forms #
Of course, it’s also possible to get banned very quickly, usually due to some sort of error on the sender’s part. maybe an integration failed and sent the wrong content, maybe a spammer was able to use the domain to send spam, or possibly a bot exploited some web forms to facilitate a denial of service attack. These large bursts of spam with an increase in spam complaints prompt Gmail to take urgent and aggressive action to prevent messages from harming others.
so don’t make yourself a victim. be proactive about who can use and trigger messages on your signup forms, for example:
- implement state-of-the-art security steps and invisible captchas on websites, with little effect on the overall user experience
- another option is to show the captcha only when a form is accessed several times through the same ip/user.
Beyond that, try not to make collecting your customers’ email addresses a required step. when people get frustrated, they fill in any random information to proceed, often leading to sending an email to a spam trap that will block their future messages.
step 4: monitor your reputation #
Configuring a dmarc policy on your domain not only forces you to reject fraudulent messages, it also sends you valuable reports about nefarious activities originating from your own domain. if a spammer exploits a vulnerability, you’ll quickly have the data you need to start protecting your sender’s reputation.
make sure you set dmarc correctly #
A word of warning: what if you’ve set up dmarc and yet gmail keeps rejecting your mail for reputation-related reasons and throws an error like this?
We’ve seen this happen recently in Postmark, and when I went to investigate I noticed that this reputation-based ISP block was often preceded by a series of DMARC bounces, like this:
Here’s the thing: just because you set up your DMARC policy, it doesn’t mean it’s implemented correctly. If something is not right in the set up, Gmail will notice and give you some DMARC-related bounces at first:
And if you still don’t take action, then Gmail will sometimes ‘upgrade’ this error to the ISP block you saw before. Sneaky!, but not unusual.
be responsive to detected reputation changes #
the best and easiest pointer is to register your dkim domain with google postmaster tools. This suite of tools shares data from Gmail directly about your messaging performance each day, including IP and domain reputation metrics. We even have a handy guide on how to interpret and respond to this reputation data, so you don’t have to guess if your hard work is paying off.
In a nutshell, gmail just wants to make the internet a nicer and safer place for its customers. By respecting your recipients’ inboxes and keeping your assets safe, gmail lockouts will be a thing of the past.
learn more about gmail bounce errors (and beyond)#
- reputation-based bounces aren’t the only gmail bounces you may encounter: you may also see bans triggered by suspicious content. we found that link shorteners may be the culprit.
- For a complete list of smtp error codes we detect in the wild and guidance on what they mean, see the postmark smtp field manual.
- back to basics: what are smtp codes and how can I fix them?