Common Email Deliverability Issues and Their Solutions

Most email deliverability issues come from four causes: broken authentication, a damaged sender reputation, a list with bad addresses, or content that looks like spam. Authentication means the SPF, DKIM and DMARC records that prove an email comes from your domain. Find your cause before you change anything, because each of these email deliverability problems has a different fix.

What you see	Likely cause	Check first	Read more
Hard bounces jump after a list import	Old, mistyped or bought addresses	Bounce codes: 5.1.1 means the mailbox does not exist (RFC 3463)	High bounce rates
Clicks drop at Gmail while other providers hold steady	Gmail spam rate or reputation	Google Postmaster Tools	Spam folder placement
Rejections that mention authentication	SPF, DKIM or DMARC failing or not aligned	The headers: `spf=pass`, `dkim=pass`, `dmarc=pass`	Check 1
Seed tests land in spam at every provider	A blocklist listing, or the content	Spamhaus and MXToolbox, then the content	Check 3
Placement fell after a platform switch	No sending history, or DNS records left for the old platform	Authentication on the new platform	Platform switch
Gmail spam rate above 0.1%, Google’s target	People who did not expect your email	Signup sources and send frequency	Sender reputation

How to Find Which Email Deliverability Issues You Have

Run four checks in this order: authentication, mailbox-provider data, a seed test, then the campaign where the drop started. Together they cover what affects email deliverability: authentication, reputation, list quality and content. Start with authentication, because Gmail says mail that misses its requirements might be rejected or delivered to spam.

Check 1: Do SPF, DKIM and DMARC Pass?

In Gmail, open a recent campaign, click More, then Show original, and look for spf=pass, dkim=pass and dmarc=pass. Fix any failure before you look at anything else.

SPF lists the servers allowed to send mail for your domain (RFC 7208).
DKIM adds a signature that receivers check against a public key in your DNS (RFC 6376).
DMARC checks alignment: it passes only when the domain in your From address lines up with a domain that passed SPF or DKIM. Its policy is p=none, p=quarantine or p=reject (RFC 9989).

A common gap: until you set up your own sending domain, many platforms sign mail with a shared domain of their own. DKIM then passes but does not align with your domain, so DMARC cannot pass. Our custom domain verification service verifies your sending domain with your email platform and updates the DNS records the platform asks for.

Check 2: What Do Google Postmaster Tools and Microsoft SNDS Show?

Google Postmaster Tools shows how Gmail users react to your mail, and Microsoft SNDS (Smart Network Data Services) shows how Outlook.com sees your sending IPs. In Postmaster Tools, watch the spam rate and the compliance status dashboard. The spam rate is the share of your inbox-delivered mail that users marked as spam. It counts only DKIM-authenticated mail (Google), one more reason to pass Check 1 first. Google plans to retire the domain and IP reputation dashboards (Google), and data only appears on days with enough Gmail volume (Google).

Microsoft SNDS only gives data for IPs you are responsible for. On a shared IP at a platform such as Klaviyo or Omnisend, rely on Postmaster Tools and your platform’s own reports.

Check 3: Where Does a Seed Test Land?

A seed test sends one campaign to test inboxes at Gmail, Yahoo, Outlook.com and other providers, and shows whether each copy reached the inbox, a tab or spam. If it lands in spam everywhere, check blocklists before you rewrite anything: the Spamhaus Reputation Checker, and the MXToolbox blacklist check, which tests over 100 blocklists. Our list of email deliverability tools compares seed-test options.

Check 4: Which Campaign or Segment Started It?

Find the first campaign or flow where bounces, complaints or clicks moved. Then look at what changed that week: a list import, a new segment, a bigger send or a new template. Judge flows and campaigns apart. If both dropped, look at authentication or reputation. If one campaign dropped alone, check its list and content.

High Bounce Rates: What Causes Them and How to Fix Them

A high bounce rate means you are sending to addresses that do not exist or cannot take mail right now. Remove hard bounces at once, then find the signup source that added them.

Bounce rate is bounces divided by emails sent, times 100. Klaviyo calls a bounce rate under 1% healthy and over 2% a sign that needs attention (Klaviyo).

The code in each bounce tells you its type: a reply code that starts with 4 is temporary, and one that starts with 5 is permanent (RFC 5321). One exception: a full mailbox can return 552 with 5.2.2. RFC 3463 says the mailbox-full code is a persistent transient failure, so treat it as a soft bounce.

Bounce type	What it means	Typical codes	What to do
Hard bounce	The mailbox or its domain does not exist	550 with 5.1.1 or 5.1.2 (RFC 3463)	Remove the address at once
Soft bounce	The mailbox is full or the server is busy	4.2.2, 552 with 5.2.2, 450 or 452	Let your platform retry, then suppress the address
Block	Refused for a policy reason, such as failed authentication	4.7.x or 5.7.x at Gmail	Fix the cause before you send again

Klaviyo suppresses an address after 7 soft bounces in a row within 2 years (Klaviyo). Mailchimp allows 7 soft bounces for a contact with no activity and up to 15 soft bounces for one with past activity (Mailchimp).

What Causes High Bounce Rates

High bounce rates usually come from bad addresses: typos at signup, fake addresses typed in for a discount, abandoned inboxes, and bought or rented lists. A sudden jump in volume can also add soft bounces. Google asks senders without a history of large volumes to avoid spikes (Google). A rise in 5.7.x blocks points to authentication or reputation, not to the list.

How to Reduce Bounce Rates

Stop bad addresses at signup, remove hard bounces as they happen, and stop mailing people before their addresses die.

Double opt-in confirms each new address with a click.
Real-time validation on the form catches typos such as gmial.com and blocks disposable addresses.
Never re-import hard bounces. Spamhaus says providers turn some dead addresses back on as spam traps after bouncing mail for a period, often 12 months or more (Spamhaus).
Clean before a large send. Klaviyo suggests a cleanup segment of anyone with at least 4 bounced emails in the last 90 days (Klaviyo).

Spam Folder Placement: How to Keep Emails Out of Spam

Emails go to spam when the provider cannot verify the sender, when recipients complain or ignore the mail, or when the content looks like spam. Check those three things in that order.

Google asks senders to keep the spam rate in Postmaster Tools below 0.1% and never let it reach 0.3% (Google). Gmail measures that rate against mail delivered to the inbox, so 0.1% is 1 complaint per 1,000 inbox deliveries (Google).

Why Emails End Up in Spam Folders

Five things send email to spam:

Failed authentication. Gmail may reject such mail or deliver it to spam (Google).
Complaints. Each click on the spam button raises your spam rate, which Gmail and Yahoo both limit.
Low engagement. Spamhaus warns that a growing share of unengaged addresses lowers your reputation and raises complaints (Spamhaus).
Spam traps. Spamhaus treats a trap hit as a sign of a data collection or hygiene problem (Spamhaus).
Content and links. Image-only emails, link shorteners and unsafe link domains add risk (see content optimization).

How to Improve Inbox Placement

Authenticate your domain, mail only people who opted in and still engage, offer one-click unsubscribe, and send at a steady rate.

Pass SPF, DKIM and DMARC with your own From domain, as in Check 1.
Add the List-Unsubscribe and List-Unsubscribe-Post headers from RFC 8058, plus a clearly visible unsubscribe link in the body.
Send at a consistent rate without bursts, as Google asks.
Suppress people who stopped engaging with a sunset policy.
Move DMARC from p=none to p=quarantine or p=reject once all your real mail passes. Microsoft recommends p=reject (Microsoft).

Gmail, Yahoo and Outlook Sender Requirements

Since February 1, 2024, Gmail has required bulk senders to authenticate with SPF, DKIM and DMARC, offer one-click unsubscribe, and keep the spam rate under 0.3% (Google). Yahoo enforces similar rules, and Outlook.com added its own on May 5, 2025 (Microsoft).

Provider	Applies to	What is required	Since	Source
Gmail	Every sender	SPF or DKIM. Valid forward and reverse DNS. An encrypted (TLS) connection. Messages formatted to RFC 5322. A spam rate below 0.3%.	February 1, 2024	Google
Gmail	Bulk senders	SPF and DKIM. DMARC at `p=none` or stronger, aligned with SPF or DKIM. One-click unsubscribe for marketing mail, with unsubscribes honored within 48 hours. A spam rate under 0.3%, and Google asks for under 0.1%.	February 1, 2024, with one-click unsubscribe due by June 1, 2024. Stricter enforcement, including rejections, from November 2025.	Google and Google’s FAQ
Yahoo	Every sender	SPF or DKIM. Valid forward and reverse DNS. A spam rate below 0.3%.	February 2024	Yahoo Sender Hub
Yahoo	Bulk senders (no volume figure published)	SPF and DKIM. A passing DMARC policy of at least `p=none`, aligned. One-click unsubscribe. Unsubscribes honored within 2 days.	February 2024	Yahoo Sender Hub
Outlook.com	Domains sending more than 5,000 emails a day	SPF and DKIM pass. DMARC at `p=none` or stronger, aligned. Failing mail goes to Junk and may be rejected.	May 5, 2025	Microsoft

Last checked: November 1, 2026.

Who Counts as a Bulk Sender?

Gmail counts you as a bulk sender once you send close to 5,000 messages or more to personal Gmail accounts within 24 hours. Mail from the same primary domain counts together, and a sender who crosses that line once stays a bulk sender for good (Google). Agencies that send for several brands should give each client its own authenticated domain, which our white-label email marketing team sets up for them.

Low Inbox Placement Rates: How to Diagnose and Fix Them

Delivered is not the same as inboxed. A delivered email can still land in spam or the Promotions tab, so measure placement with seed tests and mailbox-provider data, not with the delivery rate.

How to Identify Low Inbox Placement Rates

Look for clicks that fall at one mailbox provider while the others hold steady, then confirm the drop with a seed test and Postmaster Tools. Treat open rates with care: Apple Mail downloads email content in the background whether or not the person engages (Apple), so opens overstate reading. Customer messages about missing order confirmations are another early sign.

Gmail and Klaviyo publish these thresholds:

Metric	Healthy	Room for improvement	Needs attention	Source
Gmail spam rate in Postmaster Tools	Below 0.1%	0.1% to 0.3%	0.3% or higher	Google
Bounce rate	Under 1%	1% to 2%	Over 2%	Klaviyo
Unsubscribe rate	Under 0.3%	0.3% to 1%	Over 1%	Klaviyo
Spam complaint rate in Klaviyo’s reports	Under 0.01%	0.01% to 0.05%	Over 0.05%	Klaviyo

Klaviyo’s guide was last updated March 10, 2026.

How to Improve Inbox Placement Rates

Fix the cause your checks found, then mail your most engaged people first and widen the audience step by step.

Keep a sender name people know, and a reply address that accepts replies.
Widen slowly. Google’s advice is to start with a low volume to engaged users and increase it slowly over time (Google).

How to Build and Maintain a Strong Sender Reputation

Mailbox providers judge your sending domain and IP by complaints, bounces, engagement and authentication. You repair a reputation by sending only to people who engage and by fixing whatever drove the complaints.

To fix email deliverability issues caused by a poor sender reputation, work in this order:

Fix authentication, as in Check 1.
Cut sends back to people who opened or clicked recently.
Remove the source of the complaints, such as a bought list.
Add older segments back in steps while the Gmail spam rate stays below 0.1%.

Your domain reputation follows you to any platform. On a shared IP, the platform manages the IP’s reputation. A dedicated IP is yours alone, so a new one needs a slow start.

What Can Harm Your Sender Reputation

Five things harm a sender reputation: spam complaints, hard bounces, spam trap hits, low engagement and sudden jumps in volume. Complaints move fastest, because Gmail measures them against inbox-delivered mail (Google).

How to Build and Protect Your Sender Reputation

Authenticate your domain, warm up anything new slowly, send at a steady rate, and stop mailing people who no longer engage.

Warm up new domains and IPs. Mail your most engaged contacts first and raise volume in steps.
Mail by engagement. Segment your audience so most sends go to recent openers and clickers.
Keep message types apart. Google asks senders to use the same From address for each category of message and not to mix content types in one email (Google).
Monitor. Check the spam rate in Postmaster Tools every week.

List Quality: How to Build and Maintain a Healthy Email List

A smaller list of people who opted in and still engage beats a big list of old, bought or mistyped addresses. Bad addresses bring bounces, spam traps and complaints.

Common Email List Quality Problems

The usual problems are bought lists, spam traps, typos, disposable addresses and subscribers who stopped engaging. Spamhaus describes several kinds of spam trap (Spamhaus). Three matter most for a store’s list:

Classic traps: addresses never given to a real person.
Dead-address traps: old addresses a provider turned back on.
Typo traps: addresses at look-alike domains such as yaaho.com.

Sign of Poor List Quality	Impact on Deliverability	Recommended Action
Purchased Lists	Complaints, spam traps and blocklist risk	Delete the list and grow from your own signup forms
High Hard Bounces	Damaged sender reputation	Validate addresses at signup and remove hard bounces at once
Inactive Subscribers	Lower engagement and more complaints	A re-engagement series, then a sunset policy
Spam Traps	Blocklist listings	Fix the signup source that added them

How to Maintain a Clean Email List

Confirm addresses at signup, remove hard bounces at once, sunset people who stopped engaging, and never buy a list.

Sunset policy. Spamhaus notes that mailbox providers can look at addresses unengaged for anywhere from three to twelve months (Spamhaus). Pick a window in that range that fits how often your customers buy.
Re-engage first, in batches. Send a re-engagement email before you remove anyone, and spread it over several days rather than mailing every unengaged contact at once.
Honor unsubscribes fast. US law allows 10 business days (FTC), but Gmail expects 48 hours (Google) and Yahoo requires 2 days from bulk senders (Yahoo).

Our guide to email list cleaning covers the full routine.

Content Optimization: How to Avoid Spam Filters

To avoid spam filters, keep the email itself honest and readable, from the subject line to the links.

Common Content Problems That Trigger Spam Filters

Five content problems add spam-filter risk: misleading subject lines, image-only emails, risky links, broken HTML and heavy attachments.

Content Element	Spam Trigger Risk	Recommended Solution
Subject Line	ALL CAPS, rows of punctuation, or a fake “Re:”	Sentence case and a promise the email keeps
Images	An email that is one large image	Live text that reads with images off, and alt text
Links	Shorteners, raw IP addresses, or link text that names another site	Full links on your own domain
Formatting	Broken HTML, or no plain-text version	A tested template with a plain-text part
Attachments	Large or executable files	Host the file and link to it

Google asks every sender to format messages to RFC 5322 and to check regularly that its domain is not listed as unsafe by Google Safe Browsing (Google).

What Is the 60/40 Rule in Email?

The 60/40 rule is a rule of thumb, not a mailbox-provider requirement. It says to keep about 60% of an email as live text and 40% as images, so the email still reads when images are off (Email on Acid).

Gmail, Yahoo and Outlook.com publish no text-to-image ratio in their sender rules. In a 2014 test against 23 spam filters, Email on Acid found that the ratio did not affect deliverability once an email held 500 or more characters of text. The real risk is an email that is one large image. It shows nothing when images are blocked and gives filters no text to read.

The same name is also used for a content mix: about 60% of emails helpful and 40% promotional (Instantly).

How to Improve Email Content

Write subject lines that match the email, keep live text that reads with images off, use full links on your own domain, and add a plain-text version.

Write “Your weekly picks are here”, not “URGENT: FREE OFFER!!!”.
Build CTA buttons in live text, not as images.
Use descriptive link text, never a raw URL or a shortener.
Include an unsubscribe link. The CAN-SPAM Act requires a clear and conspicuous way to opt out (FTC).

Why Deliverability Drops After You Switch Email Platforms

Deliverability can dip after a platform switch for three reasons. The new setup has no sending history, old DNS records still point at the previous platform, or the first sends reach the whole list instead of engaged contacts.

Fix each cause before you switch:

Set up authentication on the new platform first. Add its DKIM records and SPF include, and check that DMARC aligns with your From domain.
Watch the SPF lookup limit. SPF allows at most 10 DNS lookups, and a record that needs more returns an error instead of a pass (RFC 7208). Remove the old platform’s include after its last send.
Carry over every suppression. Import unsubscribes, hard bounces and spam complainers before anyone else, so nobody who left gets mailed again.
Start with your most engaged contacts. Send the first campaigns to recent openers and clickers, then add older segments in steps, as Google advises.
Watch the Gmail spam rate and your bounce rate after each send.

For the full move, use our platform migration checklist.

How Long Does It Take to Fix Email Deliverability?

Authentication fixes work once the new DNS records are live. A damaged reputation recovers more slowly through steady sending to engaged contacts, so watch the trend in Postmaster Tools.

Fix	When you see the effect	Source
A new SPF record	Up to 48 hours to start working	Google Workspace
Gmail spam rate	Recalculated every day	Google’s FAQ
Help from Gmail’s delivery support	Available again once a bulk sender’s spam rate stays below 0.3% for 7 days in a row	Google’s FAQ

Conclusion: How to Ensure Reliable Email Deliverability

Reliable email deliverability comes from seven habits:

Authenticate with SPF, DKIM and DMARC, aligned with your From domain. Our domain authentication setup service verifies your sending domain with your email platform.
Offer one-click unsubscribe, and honor requests within 48 hours, the window Gmail and Yahoo expect.
Keep the Gmail spam rate below 0.1%.
Remove hard bounces at once.
Sunset people who stopped engaging.
Send at a steady rate, and warm up anything new with engaged contacts first.
Seed test large sends, and check blocklists when every provider drops at once.

Once you know the cause, our guide on how to improve email deliverability walks through each fix.

FAQs

What steps can I take to improve my email sender reputation?

Pass SPF, DKIM and DMARC with your own domain. Send only to people who opened or clicked recently, remove hard bounces at once, and offer one-click unsubscribe. Send at a steady rate and watch the spam rate in Google Postmaster Tools. Add older segments back in steps once the spam rate holds low.

How can I effectively reduce email bounce rates?

Use double opt-in and real-time validation at signup. Remove hard bounces as soon as they happen, never re-import them, and let your platform suppress repeat soft bounces. Clean old segments before a large send. Klaviyo treats a bounce rate under 1% as healthy.

How can I prevent my emails from going to spam?

Authenticate with SPF, DKIM and DMARC, and mail only people who opted in and still engage. Offer one-click unsubscribe, keep live text that reads with images off, and avoid link shorteners. Seed test large sends, and check blocklists if every provider sends you to spam.

What spam complaint rate is too high?

At Gmail, a spam rate of 0.3% or higher in Postmaster Tools is too high, and Google asks senders to stay below 0.1% (Google). Yahoo requires below 0.3% (Yahoo). Klaviyo flags a complaint rate over 0.05% in its own reports (Klaviyo).

Does Gmail require DMARC at p=reject?

No. Gmail requires bulk senders to publish a DMARC record, but the policy can be p=none (Google). The From domain must still align with the SPF or DKIM domain. Move to p=quarantine or p=reject once your DMARC reports show that all your real mail passes.

Why do some email platforms stop campaigns without warning?

Platform abuse checks stop sends that look risky. Mailchimp’s Omnivore disables sending to an audience whose new addresses have a high predicted bounce or abuse rate (Mailchimp). Klaviyo can disable an account after repeated bounce, unsubscribe or complaint problems, and it emails the details to the primary account owner (Klaviyo). That notice can land in an inbox nobody watches.