ISP Deliverability Guide: Gmail (Updated)
Google's Gmail might be the preeminent mailbox provider. Launched in 2004, Gmail has grown from the "new kid on the block" into one of the biggest hosts of individual email mailboxes in the world. Depending on what data you look at, you might even see Gmail as the #1 mailbox provider, at least here in the US.
Gmail's spam filtering systems incorporate user feedback and engagement. And they know what they're doing. If you are not sending wanted mail to people who requested that mail and who read that mail at high enough percentages, you're going to struggle. You won't reliably get your mail to the inbox. Their systems are too good -- their magic spam fighting robots look at metrics very closely -- and how they interpret certain metrics can even change over time! What got you to the inbox in 2019 might not be good enough to get you to the inbox today. Deliverability success at Gmail requires not only that you adhere to best practices, but it also necessitates ongoing monitoring and tweaking of your marketing program.
Gmail Has Two Domains
Google's consumer mailboxes (aka freemail or webmail are hosted at two different domains: gmail.com and googlemail.com. They are both "Gmail." The second domain was offered to some European users in the past because of trademark issues.
Google hosts mail for over 700,000 other domains, but these are not "their" domains and not consumer webmail. This is the world of Google Workspace, Google's business email hosting service. In this world, the filtering rules are more configurable by domain owners (Google customers), but it's safe to assume that some very similar version of the rules/requirements apply to both Gmail and Google Workspace email systems. Aim for suitable best practices and complying with requirements across the board, and you'll find inbox success in both business and consumer Gmail inboxes.
Spam Resource Top Five Deliverability Tips for Gmail
- DO enable email authentication. SPF, DKIM are required nowadays. Full stop. I've got a blog full of definitions and guidance on email authentication, so I won't re-define it all here. Any platform you send email from will have instructions on how to configure DKIM, SPF, or both. Implement DKIM for ESP/marketing/bulk mail (here's how on Klaviyo, for example), and implement both SPF and DKIM for your 1:1 email domains (for example, in Google Workspace or Microsoft 365). Do not assume that you're covered for DKIM authentication, just because your ESP platform might add its own DKIM signature with one of its own domains. That's not good enough.
- DO enable DMARC. This whole blog is full of guidance talking about what DMARC does and why it is important. And why "alignment" matters. After you're sure you're authenticating all mail, set yourself up with DMARC reporting, and move to DMARC with a policy of p=quarantine or p=reject. Why? To discourage bad guys from sending mail using your domain, helping you to avoid the reputation damage associated with that, both as measured by spam filters, and measured by email recipients. If somebody else sends a million hateful emails to people using your email domain, it's you that those unhappy recipients that will be mad at.
- DON'T focus on "Promotions" vs "Updates" tab placement. Google wants to place marketing mail in the "Promotions" tab and trying to outsmart them is not something you'll get away with in the long term. Instead of spending effort on an arms race of trying to outsmart shifting Gmail filters, focus on sending wanted mail and subscribers are going to read it regardless of what tab it shows up in. (And keep in mind, whichever tab it is under, it is actually in the inbox.) See also the "snake oil" section below, a warning about the folks who will try to sell you a shaky shortcut to the Primary inbox.
- DON'T buy or rent lists. Google is very sensitive to feedback from Gmail subscribers. Send mail to a purchased list, and enough people will mark that mail as spam, and Gmail's filters will pick up on that and then all your mail goes to spam. Cleaning up after you fall into this trap takes time and is not fun. Elevated spam rates have a negative impact on inbox delivery for bulk senders. Keeping your rate low also makes you more resilient to the occasional spike in complaints. And once your spam rate goes bad, it can take time for improvements to reflect positively on your filtering.
- DO focus on engagement. Gmail's filtering is heavily engagement-driven. (You will occasionally find a gadfly who swears otherwise, but they're full of beans. I am not.) If you're struggling to get solid inbox placement, a common fix is to adjust who you're sending to so that you are mailing only subscribers who have opened or clicked in the past 9-12 months. Stick to that for at least 30 days, and that will likely result in you getting solid inbox placement, and should keep your mail out of the spam folder. (If your mail truly is wanted by your subscribers.) Then you have to decide what to do about the rest of your subscriber base, the people who aren't responding. Sunsetting, for example. You can most definitely apply nuance and strategy here; take my guidance as the starting point.
I've got a whole Yahoo Mail & Gmail Sender Compliance Guide that you'll want to check out. It goes over modern Yahoo and Google bulk sender requirements in detail, with guidance on how to comply with each of those documented requirements. And for a broader look at the sender requirements facing the biggest mailbox providers, see my MAGY Sender Compliance Guide.
One of the best free tools available to ensure that you're complying with all modern email sender requirements is "Aboutmy.email" by Word to the Wise. It's simple to use, just feed it an email message from your marketing automation tool, newsletter platform, etc., and you'll get a detailed report breaking down the different technical compliance points. This is a great way to get a one-stop, multi-point inspection of specific sending infrastructure.
In fact, my experience shows me that nearly all of the time, the reason a sender's mail is going to the spam folder is because that sender didn't fully follow permission marketing best practices. There isn't some header or code you need to add that will fix a deliverability problem caused by low engagement or a lack of permission.
Don't Look for a Technical Fix to a Permission Problem
Above, I focus almost exclusively on technical requirements. Keep in mind that technical perfection does not guarantee that a message will be delivered to the inbox. It's only part of the equation.
Sure, occasionally an ESP or email platform will mess something up, and you should definitely work with them to check to see that SPF, DKIM, the list-unsub header, bounce processing, and all that other stuff are working properly (see Gmail's Sender Guidelines to learn more).
But let's be clear -- it is rare that a technical failure is the source of a deliverability issue.
This is a form of hashbusting, and it is a bad practice. Google doesn't like it. If they figure out you're doing it, they're likely to treat your messages unkindly. And it's an arms race you cannot win: the trick may work today, but Google will catch up, and your "solution" will stop working, and now you've also got a suspicious sender label attached to your domain for your trouble.
If you have to hide random code in your footer to get past a filter, you're playing a very risky game.
This includes RFC compliance failures that Google was once more tolerant of. Duplicate headers, missing required headers, broken or missing email authentication, broken DNS, these are all things that can drive Gmail to reject your mail today, even though they might have let those messages through in the past.
The lesson: "it worked fine that way yesterday" doesn't mean anything. If you're not sure whether your configuration meets all modern requirements, now is a good time to check, especially if you're seeing SMTP errors referring to RFC non-compliance.
The reason this surprises people is that DNS tends to get treated as a one-time checklist item. Set up SPF. Set up DKIM. Publish DMARC. Check the box. Move on. Never look back. But DNS records change, and infrastructure changes, and things break over time. Google now surfaces this kind of auth and RFC failure data in DMARC aggregate reporting, which gives senders visibility they never had before. Use it.
It can be hard to catch deferrals. Not every email marketing automation platform surfaces temporary delivery delays (or the 4xx SMTP error codes behind them) to their customers. Especially if an issue self-resolves after a period of time. But ignoring deferral-delivered warnings is risky; when deferrals come first, rejections can come later. Don't ignore this important warning signal.
Note also that Google discourages "bursty" traffic. Consistent pacing is better than blasting a big batch and then going quiet. Sending at a steady rate, like one message per second, is what Google wants to see, especially from newer domains undergoing IP and domain warming.
The specific things to avoid:
But there's an important change to know about. With the transition to GPT V2, IP and domain reputation indicators are gone. Instead, you now look to the "Deliverability Analysis" section, which provides more contextual guidance about what Gmail is seeing and why it might be a problem.
The Deliverability Analysis responses you might see include things like:
There's also a separate compliance status field in GPT V2, which is distinct from the Deliverability Analysis warnings. It reflects your domain's compliance state at the time you check it -- values like compliant or needs work. It's not a score and it's not tied to a specific date; it's a current-state check on whether your domain is meeting Google's requirements. Worth watching alongside the analysis warnings.
Here you'll find Google's support page for GPT.
First: not everybody will love this functionality. Some people turn it off. The Promotions tab is a precedent -- a significant chunk of Gmail users never enabled it, or disabled it after trying it. It is too soon to assume that everyone will be head over heels in love with the A.I. inbox.
Second: the machine wants to serve up what people want to read. That works in your favor, if you're a good sender. If the whole reason people signed up for your emails is because they want your specific newsletter with its specific focus, they're still going to want to read it. The A.I. inbox won't stop that from happening. If, on the other hand, you're sending simple upsells to people who were barely interested, and if your emails can be completely summarized down to a single sentence without any loss of context, then you might be right to be worried.
The bottom line: this rewards good senders and punishes not-so-good ones. Which brings it right back to the same advice as always -- send wanted, engaging mail that people actually are interested in.
Google's process has been updated. They now issue ticket numbers and review all submissions. They still don't typically respond to these submission requests, but deliverability will sometimes improve in about two weeks' time -- if merited. Which means: you have to be able to show that you're a good, or improving, sender. If you're just shoveling spam and begging for help, nothing will come of it. Make the submission, be patient, and continue to monitor deliverability.
Click here to view the whole series of Spam Resource ISP Deliverability Guides.
But let's be clear -- it is rare that a technical failure is the source of a deliverability issue.
Watch Out for Snake Oil
Speaking of "some header or code you need to add" -- there is a whole cottage industry of self-described deliverability experts who will sell you a "solution" to get your mail out of the Promotions tab and into the Primary inbox. What they're selling is a blob of code that looks nonsensical when you read it. Its only purpose is to trick Gmail's categorization systems into failing to properly classify your message, to attempt to force delivery to the Primary inbox.This is a form of hashbusting, and it is a bad practice. Google doesn't like it. If they figure out you're doing it, they're likely to treat your messages unkindly. And it's an arms race you cannot win: the trick may work today, but Google will catch up, and your "solution" will stop working, and now you've also got a suspicious sender label attached to your domain for your trouble.
If you have to hide random code in your footer to get past a filter, you're playing a very risky game.
Gmail Blocks on Sender Requirements Failures Now
In past years, Gmail's enforcement of sender requirements was more piecemeal and selective. That is no longer the case. Google warned in November 2025 that enforcement was ramping up, and they meant it. Messages that fail to meet the sender requirements now experience disruptions, including temporary (4xx) and permanent (5xx) rejections.This includes RFC compliance failures that Google was once more tolerant of. Duplicate headers, missing required headers, broken or missing email authentication, broken DNS, these are all things that can drive Gmail to reject your mail today, even though they might have let those messages through in the past.
The lesson: "it worked fine that way yesterday" doesn't mean anything. If you're not sure whether your configuration meets all modern requirements, now is a good time to check, especially if you're seeing SMTP errors referring to RFC non-compliance.
Check (and Monitor) Your DNS
If you're seeing Gmail rejections and your authentication looks fine, check your PTR records. Broken DNS catches a lot of senders off guard. During the 2025 holiday season for email marketers, the single largest driver of Gmail rejections was not spam complaints, and it was not authentication failures. It was broken or missing PTR records. Gmail alone rejected tens of millions of messages for this reason in a matter of weeks.The reason this surprises people is that DNS tends to get treated as a one-time checklist item. Set up SPF. Set up DKIM. Publish DMARC. Check the box. Move on. Never look back. But DNS records change, and infrastructure changes, and things break over time. Google now surfaces this kind of auth and RFC failure data in DMARC aggregate reporting, which gives senders visibility they never had before. Use it.
When You Get Deferred: What To Do
If you hit a temporary deferral at Gmail, don't keep hammering away. Google's guidance is specific, and it's worth following:- Stop sending for at least 10 to 15 minutes.
- Identify the cause. If the deferral doesn't specify whether you exceeded a DKIM, SPF, or IP quota, assume all three are affected.
- Send a single test message. If it fails, wait another 10 minutes.
- If it succeeds, resume sending at a volume below the limit that triggered the deferral, and stay there for 24 hours before ramping back up.
It can be hard to catch deferrals. Not every email marketing automation platform surfaces temporary delivery delays (or the 4xx SMTP error codes behind them) to their customers. Especially if an issue self-resolves after a period of time. But ignoring deferral-delivered warnings is risky; when deferrals come first, rejections can come later. Don't ignore this important warning signal.
Note also that Google discourages "bursty" traffic. Consistent pacing is better than blasting a big batch and then going quiet. Sending at a steady rate, like one message per second, is what Google wants to see, especially from newer domains undergoing IP and domain warming.
Don't Get Clever
Google has been tightening enforcement around deceptive creative, and some of this catches legitimate senders who didn't realize they were doing anything wrong. You'll find this called out as point seven on Google's own "Top 10 Gmail sender issues" guide.The specific things to avoid:
- Fake Re: or Fwd: prefixes on messages that aren't actually replies or forwards.
- Display names that impersonate a reply thread, like "User (2)" or a bracketed number that implies a new message count.
- Display names that include the recipient's name.
- Emojis or images used to imply verification, like a checkmark next to your brand name.
- Display names that include subject-line content, like "TIME IS RUNNING OUT (SALE)" or "Important Update."
GPT: Watch the Deliverability Analysis
Google has a reputation portal called Google Postmaster Tools (GPT). Register your domains here and you'll get varying levels of information about how Gmail sees your sending.But there's an important change to know about. With the transition to GPT V2, IP and domain reputation indicators are gone. Instead, you now look to the "Deliverability Analysis" section, which provides more contextual guidance about what Gmail is seeing and why it might be a problem.
The Deliverability Analysis responses you might see include things like:
- Users signal they want to get your email messages (good!)
- You don't meet our sender requirements (technical configuration?)
- Users signal that they don't want to get your email messages (you're making people angry)
- Users don't take action on your messages (they don't care about you)
- Your spam rate is above 0.1% (you're making people really angry)
There's also a separate compliance status field in GPT V2, which is distinct from the Deliverability Analysis warnings. It reflects your domain's compliance state at the time you check it -- values like compliant or needs work. It's not a score and it's not tied to a specific date; it's a current-state check on whether your domain is meeting Google's requirements. Worth watching alongside the analysis warnings.
Here you'll find Google's support page for GPT.
The A.I. Inbox
You may have heard that Gmail is entering the "Gemini era", with A.I.-driven inbox functionality. Senders have been nervous about this, wondering whether recipients will even see their email marketing messages any more. I wrote about this back in January and I'll summarize my thoughts here.First: not everybody will love this functionality. Some people turn it off. The Promotions tab is a precedent -- a significant chunk of Gmail users never enabled it, or disabled it after trying it. It is too soon to assume that everyone will be head over heels in love with the A.I. inbox.
Second: the machine wants to serve up what people want to read. That works in your favor, if you're a good sender. If the whole reason people signed up for your emails is because they want your specific newsletter with its specific focus, they're still going to want to read it. The A.I. inbox won't stop that from happening. If, on the other hand, you're sending simple upsells to people who were barely interested, and if your emails can be completely summarized down to a single sentence without any loss of context, then you might be right to be worried.
The bottom line: this rewards good senders and punishes not-so-good ones. Which brings it right back to the same advice as always -- send wanted, engaging mail that people actually are interested in.
Contacting Google for Help
Google has a remediation request submission process (click here), where you can submit a sample message, state your case, and request that they reconsider spam folder placement (or blocking) of your messages. Use it. But only AFTER you're sure that you're doing everything right. If you're buying lists or trying to email people who haven't responded in years, you're wasting your time. But if you ARE doing everything right, and you think Google is unfairly filtering your messages, they do offer this review process.Google's process has been updated. They now issue ticket numbers and review all submissions. They still don't typically respond to these submission requests, but deliverability will sometimes improve in about two weeks' time -- if merited. Which means: you have to be able to show that you're a good, or improving, sender. If you're just shoveling spam and begging for help, nothing will come of it. Make the submission, be patient, and continue to monitor deliverability.
Deliverability Evolves Over Time
Google tweaks their spam filters over time, resulting in new error messages, new reasons for deferrals, and new explanations around how best to comply with ever-evolving best practice requirements. If you want to stay on top of all of this, sign up for the Spam Resource newsletter, where I share stuff like this often.Click here to view the whole series of Spam Resource ISP Deliverability Guides.