Email deliverability is the percentage of your sends that reach the inbox rather than the spam folder or a bounce. To increase it, you need to work on three categories: list quality (who you're sending to), authentication (proving who you are), and sending behavior (how you behave as a sender). Fixing all three in the wrong order wastes time. Fix list quality first.
EmailAddress.ai handles list quality through bulk email verification and catch-all domain scoring. This page covers what drives deliverability problems and what order to address them.
Why is your email deliverability dropping even if you haven't changed anything?
Deliverability degrades passively. Your list decays at 2-3% per month in B2B, meaning hard bounces accumulate even without a change in your sending behavior. Gmail, Outlook, and Yahoo update their spam filtering models continuously, so content or volume patterns that previously passed through cleanly can start triggering filters with no action on your part.
The first signal is usually a drop in open rates. If your open rate has declined more than 5 percentage points over 90 days without a change in subject line strategy, your mail is likely moving from inbox to promotions or spam rather than being ignored by recipients who used to open. Check your spam placement rate directly if your ESP provides it, or use a seed testing tool to confirm where mail is landing.
How does list quality affect email deliverability?
List quality is the fastest lever. Sending to invalid, inactive, or spam-trap addresses is the primary cause of deliverability problems for B2B senders. Here's how each category damages deliverability:
- Hard bounces: Invalid addresses return a permanent delivery failure. Most ESPs suspend accounts that hit 5% hard bounce rate. Even at 3%, inbox providers begin weighting your domain as a poor sender. One bulk send to an unvalidated purchased list can permanently damage a sending domain that took months to build up.
- Spam traps: Addresses operated by blocklist organizations to identify senders with poor list hygiene. Hitting a spam trap does not generate a bounce, so you won't see it in your bounce report. It shows up as sudden deliverability degradation and potential domain blacklisting.
- Low-engagement addresses: Mailboxes that have not opened in 180+ days send negative engagement signals to inbox providers. Gmail's algorithm in particular weighs per-recipient engagement when deciding inbox vs. spam placement. A list full of people who never open is a deliverability liability even if every address is technically valid.
The fix: validate your list before every campaign using a tool like EmailAddress.ai, suppress anyone who hasn't opened in 6 months, and remove hard bounces permanently within 24 hours of a campaign send.
What authentication records do you need for inbox placement?
Since February 2024, Google and Yahoo require bulk senders (over 5,000 messages per day) to have valid SPF, DKIM, and DMARC records. Without these, Gmail routes mail to spam or rejects it outright. Even below the 5,000/day threshold, missing authentication records are a significant negative signal.
- SPF (Sender Policy Framework): A DNS record that lists which servers are authorized to send email on behalf of your domain. Check yours at MXToolbox. Make sure your ESP's sending IPs are included.
- DKIM (DomainKeys Identified Mail): A cryptographic signature added to your outbound mail that proves the message was not altered in transit. Your ESP should provide a DKIM key to add to your DNS. Most major ESPs (HubSpot, Mailchimp, Klaviyo) configure this during setup, but confirm it is active on your sending domain.
- DMARC (Domain-based Message Authentication, Reporting, and Conformance): A policy that tells receiving servers what to do with mail that fails SPF or DKIM. Start with p=none to collect reports, then move to p=quarantine once you have confirmed your legitimate mail streams are passing. p=reject is the most protective setting for an established sending domain.
How does your sending volume and frequency affect deliverability?
Inbox providers build a reputation model for your sending domain based on volume, consistency, and engagement over time. Sudden volume spikes are one of the most common causes of spam folder placement because they look like a compromised account or a purchased list being activated.
If you have a new sending domain or have not emailed in several months, warm it up by starting at 200-500 emails per day and increasing volume by no more than 20-30% each week. Send only to your most engaged recipients during warm-up. This establishes a positive engagement history before you scale to larger sends.
Consistency matters more than frequency. Sending 10,000 emails every Tuesday is less risky than sending 0 for six weeks, then 50,000 for a campaign, then 0 again. Irregular patterns trigger scrutiny from spam filters.
What content factors damage email deliverability?
Spam filters have become sophisticated enough that keyword-based filtering is largely obsolete. Modern filters look at content patterns in combination with sender reputation. That said, certain content characteristics remain consistent red flags:
- Heavy use of images with minimal text (a common trick used by spammers to avoid text-based filters)
- Misleading subject lines that do not match the email body
- Missing or broken unsubscribe links
- Link shorteners that obscure the destination URL
- HTML-only emails with no plain text version
For B2B cold outreach specifically, plain text or minimal-HTML emails consistently outperform heavily designed templates on inbox placement. This is partly because sophisticated spam filters treat heavily formatted emails from unknown senders as lower-trust, and partly because plain text simply bypasses many corporate email filters that inspect HTML.
How do you recover deliverability after a spam complaint spike?
A spike in spam complaints (above 0.3% in a single campaign) requires immediate action. Stop sending to the segment that generated the complaints. Run the list through EmailAddress.ai to identify and suppress the highest-risk addresses. Audit your unsubscribe flow to ensure it works correctly and processes immediately.
After suppressing the problem addresses, send a small re-engagement campaign (under 1,000 addresses) to your most engaged segment before resuming full volume. This rebuilds a positive engagement signal with inbox providers before you scale back up. Plan on 2-4 weeks of reduced volume while reputation recovers.
Frequently asked questions about email deliverability
What is a good email deliverability rate?
Inbox placement rates above 90% are considered healthy for B2B senders. Below 85% indicates a deliverability problem worth investigating. Hard bounce rates should stay below 2% on every campaign. A spam complaint rate above 0.1% triggers review by most ESPs, and above 0.3% can result in sending suspensions.
How do I check my current email deliverability rate?
Your ESP's reporting shows open rates and bounce rates, but not inbox vs. spam placement. To test inbox placement specifically, use a seed testing service that sends your campaign to test addresses across major providers (Gmail, Outlook, Yahoo) and reports where each one lands. MXToolbox and GlockApps offer this type of testing.
Does email list validation directly improve deliverability?
Yes. Removing invalid addresses before sending reduces your hard bounce rate, which is one of the primary signals inbox providers use to assess sender reputation. EmailAddress.ai also flags spam trap addresses and low-score catch-all domains that generate silent non-delivery, which improves your overall engagement rate even when bounce counts look acceptable.
How long does it take to recover from a deliverability problem?
Minor deliverability drops from an elevated bounce rate typically recover in 2-4 weeks with corrected list hygiene and consistent low-volume sending. Domain blacklisting takes longer, often 4-8 weeks after requesting removal from blocklists like Spamhaus or Barracuda. Reputation damage from sustained spam complaint spikes is the slowest to recover and may require switching to a subdomain for sending.
Can I improve deliverability without changing my list?
Authentication records (SPF, DKIM, DMARC) can improve deliverability independently of list quality, particularly if your current setup is missing or misconfigured. But list quality problems create deliverability floors that authentication fixes cannot overcome. If your list contains 10% hard invalids and 15% low-engagement addresses, authentication improvements alone will not move your inbox placement rate significantly.
Where to start if your deliverability has already dropped
The fastest lever is list quality. Run your list through EmailAddress.ai bulk verification to remove hard invalids and flag low-score catch-all addresses. Then check your authentication records at MXToolbox and confirm SPF, DKIM, and DMARC are correctly configured. Then audit your unsubscribe flow and suppression list. Most deliverability recoveries follow that order. For context on how Gmail specifically evaluates sender reputation, understanding which campaign metrics actually signal a deliverability problem is worth reading before your next send. To run verification on your list today, contact the EmailAddress.ai team.