If you're searching for how to stop emails going to spam, you're probably staring at open rates that used to be fine and now aren't, and the honest answer is that no single fix does it, it's a stack of smaller things that Gmail and Outlook add up before deciding where your mail lands. I've gone through this stack on hundreds of audits, and the order below is roughly how much each step tends to move the needle, starting with the one almost everyone gets wrong first: authentication.
Every major mailbox provider checks three DNS records before it even reads the subject line: SPF, DKIM, and DMARC. SPF tells Gmail which servers are allowed to send mail on your domain's behalf, DKIM signs the message so it can't be tampered with in transit, and DMARC tells the receiving server what to do if either of those checks fails. Miss one, or set one up loosely, and you're sending mail that looks unverified even if every word of it is legitimate.
This is usually a one-day job with your DNS provider, and it's the first thing I check on every audit because it's the most common reason a domain that used to land fine suddenly doesn't. If you've added a new sending tool, like a CRM or a cold email platform, and didn't update your SPF record to include it, that alone can tank delivery. Walk through the full setup in this SPF, DKIM, and DMARC guide if you haven't touched your DNS yet.
Most sending platforms give you a shared return-path, also called a bounce domain, by default, which means your reputation is tied to everyone else using that platform. A custom return-path domain, something like mail.yourdomain.com, puts your bounces and reputation entirely under your own name. It's a small DNS change but it separates you from the neighbors, good or bad, on the same sending infrastructure.
Mailbox providers don't trust volume, they trust volume that grows the way a real sender's would. A brand new domain, or an old domain that hasn't sent much mail in months, gets treated with suspicion the moment it tries to send thousands of emails on day one, because that's exactly the pattern a spammer would follow.
Start small, something like 50 to 200 emails a day to your most engaged subscribers, and increase over two to four weeks. What you're doing is building a track record Gmail and Outlook can point to: this sender starts small, gets opened, doesn't get marked as spam, and slowly earns the right to send more. I've written up the warmup tools I'd actually recommend if you want to skip the manual version.
Even on an established domain, a sudden jump in send volume, say from a list purchase or a re-engagement blast, reads as a red flag. If you need to scale up fast for a launch, split it across a few days rather than one send, and lean on your most active segment first.
Deliverability isn't really about your content, it's about how the people you're mailing behave once it lands. Gmail watches open rates, deletes without opening, and spam complaints per domain, and a list full of addresses that never engage drags that signal down for everyone else on the list too.
A hard bounce means the address doesn't exist, and continuing to mail it after the first bounce tells the receiving server you're not paying attention to your own list. Subscribers who haven't opened anything in 90 to 180 days are a softer problem, but they still count against your engagement rate, and I'd rather see you win them back than let them sit there. There's a full process in how to clean an email list that separates truly dead addresses from ones worth one more re-engagement attempt.
Single opt-in fills your list faster but it also lets in typos, fake addresses, and people who forgot they signed up, all of which show up later as spam complaints. Double opt-in costs you some signups up front in exchange for a list that's actually going to open your mail, which is the trade every deliverability-conscious sender should be making.
Content filters have gotten less about individual spammy words and more about the whole pattern of a message, but a handful of habits still hurt you.
Phrases like "act now" or "100% free" in all caps with three exclamation points aren't going to sink you on their own anymore, but stacked together with a wall of red text and a giant discount banner, they add up to a message that pattern-matches to spam. I keep a running list in spam trigger words to avoid if you want to sanity check a subject line before you send.
An email that's a single giant image with no real text gives filters nothing to read except a file, which is itself a pattern spam has used for years to hide content. Keep a healthy amount of actual text, and avoid shortened links like bit.ly, since filters can't see where they resolve to and treat that opacity as risk.
Consistency is a signal on its own. A domain that sends every Tuesday and Friday at 9am builds a rhythm that mailbox providers learn to expect, and expected mail gets less scrutiny than mail that shows up erratically.
If you've gone quiet for two months and then send five campaigns in a week, that spike looks like a compromised account or a purchased list, even if it's just you catching up. Spread re-launches out and ease back into a normal cadence.
"noreply@" addresses and generic from names read as automated, and automated reads as lower priority to a filter deciding between Primary and Promotions. Sending from a real name, with a reply-to that actually gets checked, helps on both the spam side and the Promotions tab side, since Gmail's categorization also looks at whether a message looks like person-to-person mail.
You can do everything above correctly and still drift out of good standing over time, so this part isn't optional, it's ongoing.
It's free, it's built by Gmail specifically to show you your own domain reputation, spam rate, and IP reputation, and most senders never open it until something's already wrong. Five minutes a week catches problems while they're small.
A single bad campaign or a compromised sending tool can get your domain or IP listed on a blacklist, and the listing itself becomes a reason mail gets rejected even after you've fixed the underlying issue. Check your status and file removal requests promptly, there's a walkthrough in how to remove a domain from a blacklist.
Most senders see measurable improvement within one to two weeks of fixing authentication and slowing down volume, but a full recovery from a damaged sender reputation can take four to eight weeks of clean sending.
No, but a campaign with a high complaint rate or a lot of hard bounces can hurt your reputation for a few weeks, and repeating that mistake is what turns a temporary dip into a lasting problem.
Rarely on its own, because the underlying reputation issues, whether that's list hygiene, authentication, or engagement, follow your domain rather than the platform you're sending from.
Run your domain through the free Inbox Scorecard and I'll show you exactly which step is holding you back, or grab a full deliverability audit if you want the whole picture in one pass.