Why Email Deliverability Collapsed After My Host Changed IP Ranges and the DNS and SPF Patch That Recovered Trust

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In the ever-evolving landscape of email deliverability, even a minor infrastructure change can ripple through your entire communication chain in unexpected ways. Many businesses rely heavily on email as their primary means of engaging with customers, partners, and leads. So when a host changes IP ranges without adequate coordination or configuration, the results can be disastrous — lost trust, emails directed to spam folders, or worse, emails not sent at all.

TL;DR

After a web host changed their IP ranges, my email deliverability tanked. Messages started landing in spam folders or getting blocked entirely. The root cause was a mismatch in DNS and SPF records that failed to authorize the new IPs. Once I patched my DNS and SPF records to properly reflect the new sending IP range, trust was re-established and things returned to normal.

What Happened When the IPs Changed?

It all started when my web hosting provider migrated their mail servers to a different data center, which included a major change in IP addresses for outbound email. I received a routine email about “infrastructure improvements,” but didn’t think much of it. After all, aren’t such changes handled seamlessly?

The answer: not always. Within 24 hours, I realized that something was off. My transactional emails from the website weren’t being received, and campaign open rates dropped from around 30% to a pitiful 5%. Digging into the headers of test emails I sent to my personal accounts, I quickly found the problem: the new sending IPs were not authorized in the server’s SPF (Sender Policy Framework) record.

What Is SPF and Why It Matters

SPF is part of a broader effort to authenticate the source of email messages. It tells receiving servers which IP addresses are allowed to send emails on behalf of your domain. If your mail originates from an IP not listed in the SPF record, it fails SPF checks — a red flag to inbox providers like Gmail, Outlook, and Yahoo.

  • Pass – when the sending IP is listed in the SPF record
  • Fail – when the sending IP is not included, indicating possible spoofing
  • SoftFail – a warning level failure, often sending emails to spam folders

Before the IP range switch, my SPF record looked something like this:

v=spf1 ip4:192.168.1.1 include:spf.mailprovider.com -all

After the host made the change, email started to be sent from an entirely different IP range — something like 203.0.113.x — but my SPF record didn’t reflect that. Thus, email receivers couldn’t verify the authenticity of my messages.

Why Email Providers Block Unknown IPs

Email services are constantly battling spam, phishing, and spoofed messages. They rely on several signals to determine whether an incoming message is trustworthy, including:

  • SPF validation
  • DKIM authentication
  • DMARC alignment
  • Reverse DNS lookups
  • IP and domain reputation tracking

SPF is one of the most immediate and binary signals. Fail an SPF check, and an email provider like Gmail may outright block your message or relegate it to the spam folder with a warning message like “This message couldn’t be verified.”

The Trail of Clues: Diagnosing the Problem

I used a number of testing tools to piece together the problem:

  • MXToolbox to verify SPF records and look for failures
  • Gmail’s “Show Original” feature to review authentication results in headers
  • Mail-Tester.com to simulate deliveries and score headers

Here’s an example of the SPF Failure result I was seeing:

Received-SPF: softfail (google.com: domain of transitioning info@mydomain.com does not designate 203.0.113.2 as permitted sender)

Beneath the technical jargon lies one clear message: I was sending mail from an IP that the internet had no reason to trust.

The DNS & SPF Fix That Recovered Trust

Once I realized the issue, the fix was fairly straightforward — but required precise DNS adjustments.

Step 1: Get the New IP Ranges from the Host

I contacted the hosting company and asked for the full list of new outbound email IPs. They provided a range like:

203.0.113.0/24

Step 2: Update the SPF Record

I added the new range manually to my SPF record to authorize it:

v=spf1 ip4:192.168.1.1 ip4:203.0.113.0/24 include:spf.mailprovider.com -all

This change told receiving servers that email from both the old and the new ranges could be considered safe and legitimate.

Step 3: Propagate the Record

Although DNS propagation can take up to 48 hours, in practice major providers start recognizing SPF updates within a few hours. I used DNS Checker to confirm updates across global name servers.

Step 4: Re-Test

Retesting with tools like Mail-Tester and sending emails to Gmail confirmed successful SPF passes and inbox placement returned to normal. It wasn’t instant, but within 12 hours, my open rates started climbing again.

Lessons Learned and Best Practices

There are a few invaluable lessons from this experience:

  1. Always monitor your domain’s SPF, DKIM, and DMARC alignment. Treat them as part of your uptime dashboard.
  2. Proactively audit your host’s outbound IP addresses, especially when notified of backend infrastructure changes.
  3. Use include mechanisms like include:spf.mailprovider.com carefully. They simplify SPF records, but when hosts change IPs, you still need to ensure proper coverage.
  4. Test new records before assuming they’re working. Don’t just edit and forget. Use independent tools and send test messages to multiple providers.

One final tip: Don’t set your SPF with a hard fail (-all) unless you’re absolutely sure all valid servers are listed. Using ~all (a softfail) is safer during transitions.

Going Beyond SPF: Full Authentication Strategy

While this issue was rooted in SPF, a holistic email authentication strategy today involves 3 key components:

  • SPF – Authorizes IPs
  • DKIM (DomainKeys Identified Mail) – Signs email content with cryptographic signatures
  • DMARC – Specifies how receiving servers should treat messages failing SPF or DKIM

Once my SPF problem was solved, I also double-checked DKIM and DMARC to reinforce trust. Adding an aggressive DMARC policy like p=reject tells inboxes, “If the email fails checks, don’t just spam it — bounce it.” But be cautious and test thoroughly before rolling out such strict policies.

Conclusion

Email deliverability isn’t a set-and-forget process. Infrastructure shifts — like changing IP ranges — can silently sabotage your communications, damaging your brand’s trust and reach. Actively monitoring and quickly patching SPF records through DNS can prevent days of lost messages and engagement.

If you suspect falling open rates, always start by looking under the hood at authentication records. Sometimes it’s not your content or frequency — it’s a matter of trust, and trust is forged one record at a time.