Email Deliverability Guide: Why Emails Go to Spam and How to Fix It

Marketing emails usually go to spam because of missing SPF, DKIM or DMARC records, too many spam complaints, old or unengaged lists, or a sudden jump in volume. Fix authentication first, then send only to your most engaged contacts while your reputation recovers.

Email deliverability is whether your emails reach the inbox, not the spam folder and not a silent rejection. It decides whether everything else in your email marketing works: the best subject line in the world sells nothing from the spam folder. The good news is that deliverability mostly comes down to a short list of things you control.

This guide explains how inbox providers decide where your mail goes, the most common reasons emails land in spam, and what to do about each one. It ends with a checklist and a section on fixing a sudden drop.

Your email tool's "delivered" number only means the receiving server accepted the message. It might still have gone to spam or the Promotions tab. Inbox providers don't tell senders where each message landed, so you have to read the signals: falling opens and clicks across Gmail or Outlook addresses, a rising spam complaint rate, or more bounces than usual. Compare your numbers with published email benchmarks.

Inbox providers weigh three things: whether your mail is really from you (authentication), how people have reacted to your past mail (reputation), and whether this message looks like what people want (engagement and content). Since 2024 the big three have also set written rules for bulk senders. We checked their own pages on October 19, 2026:

• Gmail: Google's email sender guidelines require senders of more than 5,000 messages a day to personal Gmail accounts to set up SPF, DKIM and DMARC (a policy of "none" is allowed), align the From domain with SPF or DKIM, support one-click unsubscribe in marketing messages, and keep the spam rate reported in Postmaster Tools below 0.30%. Google's guideline is to stay below 0.10%.
• Yahoo: Yahoo's sender best practices ask bulk senders for SPF and DKIM, a valid DMARC policy of at least p=none, a working one-click unsubscribe header, unsubscribes honored within 2 days, and a spam rate below 0.3%.
• Outlook: Microsoft's requirements for high-volume senders for Outlook.com, Hotmail and Live addresses (more than 5,000 emails a day) took effect on May 5, 2025: SPF and DKIM must pass and DMARC must be published at p=none or stronger.

SPF lists which servers may send for your domain. DKIM adds a signature that proves the message wasn't changed. DMARC tells receivers what to do when a message fails, and sends you reports. Together they stop others from sending mail as you, and they are now required for bulk senders. Our guide to SPF, DKIM and DMARC explains each record and how to publish it.

Your reputation is tied to your sending domain and the servers you send from. It goes up when people open, click and reply, and down when they ignore, delete or report your mail. A few habits protect it:

• Send most campaigns to contacts who opened or clicked in the last few months. Because Apple Mail privacy protection opens emails automatically, weigh clicks and orders too.
• Keep a steady sending rhythm. Long silences followed by big blasts look suspicious.
• Use a subdomain (like mail.yourstore.com or news.yourstore.com) for marketing if your tool supports it, so marketing problems don't touch your everyday business email.
• Watch your spam complaint rate in Google Postmaster Tools and act long before it reaches 0.3%.

A domain with no sending history, or one moving to a new tool, needs time to earn trust. Start by sending to your most engaged contacts, then widen the audience a little each day or week over a few weeks. Before a big sale, raise volume steadily in the weeks before rather than all at once on the day. See our Black Friday email and SMS checklist for a timeline.

• Remove hard bounces right away: Addresses that don't exist hurt your reputation every time you send to them.
• Watch soft bounces: Full mailboxes and temporary errors are fine once; repeated soft bounces should be suppressed.
• Suppress complainers: Anyone who reports spam should never get marketing again.
• Sunset inactive contacts: Send a last re-engagement message to people who haven't engaged in months, then stop emailing those who still don't respond. See how to clean your email list.
• Never buy lists: Bought lists contain spam traps and people who never agreed to hear from you.
• Keep suppressions on import: When you move tools, bring unsubscribes and bounces with you.

• A subject line that matches what's inside.
• A recognizable From name and an address on your own domain that can receive replies.
• Real text, not one big image.
• Links on your own domain or your tool's tracked domain, not public link shorteners.
• A clear unsubscribe link, and a one-click unsubscribe header added by your tool.

• Check that SPF, DKIM and DMARC still pass. DNS changes, new tools or a domain move often break them.
• Look at your last few sends: did you mail an old segment, import a list or jump in volume?
• Check Google Postmaster Tools for spam rate and reputation changes.
• Pause sends to unengaged contacts and send only to your most engaged for a week or two.
• Check whether your domain or sending IP appears on a public blocklist, and follow the list's removal steps.

• SPF, DKIM and DMARC published and passing; From domain aligned.
• One-click unsubscribe header and a visible unsubscribe link in every marketing email.
• Spam complaint rate well under 0.3%, ideally under 0.1%.
• Hard bounces, complainers and unsubscribes suppressed automatically.
• Inactive contacts sunset on a schedule.
• New domains and big events warmed up over weeks.
• Most campaigns sent to engaged segments.
• Content that matches its subject line, with real text and your own link domains.

SmartyTap builds these habits into sending. It checks your sending domain's DNS records, including DKIM and DMARC, and ramps up new sending domains with a warm-up schedule. It adds one-click unsubscribe, suppresses bounces and complaints automatically, processes feedback loops from inbox providers, and helps you keep your list clean. Smart Sending skips anyone who got an email from another campaign in the last 16 hours, and segments make it easy to send to engaged contacts first.

SmartyTap Starter is $20 a month for 2,500 contacts, 25,000 emails and 250 SMS credits/segments. Pro is $199 a month (or $1,990 a year) for 25,000 contacts, 250,000 emails and 2,500 SMS credits/segments. One credit covers one segment and costs 2¢. New workspaces need a paid plan to send, and there's no free trial. See SmartyTap pricing.

Glossary: email deliverability, sender reputation and spam complaint rate. Set up step by step in the docs: email domain authentication, sending-domain warm-up and Smart Sending. Read next: SPF, DKIM and DMARC explained, email marketing for Shopify and welcome email series.

The most common reasons are missing SPF, DKIM or DMARC records, too many spam complaints, sending to old or unengaged contacts, and sudden jumps in volume. Fix authentication first, then send to your most engaged contacts while your reputation recovers.

Google and Yahoo both set 0.3% as the limit for bulk senders, and Google's guideline is to stay below 0.1% (checked October 19, 2026). Most healthy senders sit far below either number.

Usually a few weeks of steady, growing sends, starting with your most engaged contacts. The more mail you plan to send, the longer the ramp should be.

Inbox placement isn't reported directly, so watch the signals you can see: bounces should be low and stable, spam complaints far under 0.1%, and clicks steady across Gmail, Yahoo and Outlook addresses. A sudden drop at one provider usually points to a reputation problem there.