Case study: How we recovered our domain reputation after the delivery dropped to 80%

Email deliverability issues rarely start with a single bad campaign, and that is exactly what this case is all about. What happened was that our delivery rate dropped from a stable 99.8%-99.9% to around 80%, after which open rates followed, and inbox providers began rejecting our emails.

In this case study, our marketer explains what went wrong, how the problem was detected early, and which steps helped us recover our domain reputation, restore inbox placement, and bring email performance back to normal. We’re sharing this experience so that other teams can spot similar risks sooner and avoid repeating the same mistakes.

What changed and how the issue was detected

The problem didn’t appear suddenly. At first, it looked like a normal fluctuation in metrics, but the pattern became clear once we looked at both the delivery and reputation signals. Because we already had a routine for checking key indicators, we promptly noticed the change before the delivery fully collapsed.

What our normal baseline looked like

Before the incident, our email performance was stable and predictable:

• delivery rate at 99.8%-99.9%;
• open rate holding of around 25%;
• bounce rate within 1-2%.

These numbers had been consistent for a long time, so any deviation stood out quickly.

The first warning signals

The first sign of trouble was a sudden drop in delivery, and this did not stop at one dip; rather, it continued to fall over several sends. 

Soon after that, other metrics followed:

• delivery rate dropped sharply and kept falling;
• open rate declined, because fewer emails reached inboxes or even ended up in spam;
• bounce rate increased, and mailbox providers started returning errors, including 550 5.7.1.

At this stage, the issue was clearly unrelated to email content. Messages were either blocked or filtered before recipients could even see them.

Why Postmasters were critical

Postmasters played a key role in confirming what was happening. We check them twice a week, at the beginning and at the end of each week, and we always account for a reporting delay of up to three days.

When we reviewed the data, the situation became obvious:

• both IP reputation and domain reputation dropped to “Bad”;
• “Bad” is the lowest possible status, with no room left to fall further.

At that point, seeing both signals turn red simultaneously explained why delivery was collapsing rapidly. It also confirmed that we were dealing with a reputation issue, not a temporary metric anomaly.

What caused the collapse

Once we confirmed that this was a reputation issue, the next step we took was to understand exactly what triggered it. We found that the root cause was not hidden deep in technical settings or content quality — it actually came down to how and when we sent emails.

The sending behavior that triggered it

When we reviewed the sending activity around the same time, the metrics started to fall, and two campaigns immediately stood out:

• two campaigns were sent to a much larger (х4) audience than usual;
• the domain was not prepared for that volume increase;
• sending activity spiked sharply within a short time window.

Why the impact was so severe

The same action did not always lead to such a dramatic outcome. However, the reason it did in this case was the state of our infrastructure at that moment:

• IP reputation issues already existed from previous months;
• emails were sent from shared IPs with other senders;
• some of those neighbors had poor sending practices.

Based on the reasons listed above, the domain reputation collapse did not happen in isolation. The drop in domain trust was stacked on top of an already weakened IP reputation. Together, these factors almost completely destroyed our credibility as a sender in the eyes of mailbox providers.

How inbox providers reacted

Once reputation signals crossed into a critical zone, mailbox providers responded quickly. At that point, the issue was no longer about individual campaigns. It became a trust problem between the sender and the inbox providers.

What happened at the provider level

As soon as trust dropped, inbox providers changed how they handled our traffic:

• trust in us as a sender was reduced;
• filtering became much stricter, and part of the traffic was blocked;
• some providers returned hard errors, including 550 5.7.1, which made delivery impossible for those recipients.

These reactions were consistent across providers and aligned with what we saw in Postmasters.

How this affected email metrics

Provider-side restrictions quickly translated into visible metric changes:

• delivery rate stalled at around 80% and showed signs of dropping even further;
• open rate fell from 25% to 11%, simply because emails stopped reaching inboxes;
• bounce rate and complaints grew rapidly and peaked at roughly 20%.

At this stage, content quality no longer mattered. Even strong emails could not perform well because inbox providers were actively limiting or rejecting delivery.

First containment steps to limit damage

Once it was clear that reputation was the core issue, the priority shifted to stopping further damage. The goal was to reduce risky signals immediately while keeping essential email flows running.

Pausing high-risk activities

The first action was to stop everything that could make the situation worse:

• all manual promotional campaigns were paused;
• reactivation campaigns were fully disabled.

The decision was based on the fact that these sends usually go to broader or colder audiences. Continuing them at that point would have pushed more negative signals to inbox providers and made recovery much harder.

Protecting essential emails

At the same time, we could not afford to stop service communication. Some emails are part of core product flows and must keep working.

To protect them, a couple of steps were taken:

• service and transactional triggers were moved to a warmed subdomain;
• x10 lower sending limits were accepted to keep key flows alive.

Implementing these steps bought us time to work on recovery without breaking subscription renewals, account confirmations, or other system emails.

Why the subdomain switch worked

The subdomain played a key role in damage control:

• its reputation dropped only slightly and stayed within an acceptable range;
• problems on the main domain did not fully transfer to it;
• critical emails continued sending without interruption.

Fixing the infrastructure problem

However, containment alone was not enough. The next step was to deal with the infrastructure issues that made the collapse so severe in the first place.

Why shared IPs had to be abandoned

We already knew that IP reputation had been unstable for months before this incident. The main reasons were structural:

• reputation depended partly on other senders;
• earlier IP problems had already appeared and were only partially resolved;
• recovery on shared IPs would always stay fragile.

Even with careful sending, we knew that we could not fully control what happened on the same IP range.

Moving to dedicated IPs

The only reliable option was to move to dedicated IPs to achieve the following:

• full control over IP reputation;
• reputation tied only to our own emails;
• clearer diagnostics when something goes wrong.

There was no attempt to rescue damaged IPs. In this case, performing a clean reset with dedicated IPs was faster and safer than trying to fix a setup that we did not fully control.

Rebuilding domain reputation step by step

After stopping risky sends and fixing the IP setup, the hardest part began: earning back trust in the main domain. We realized that this process could not be rushed, and every step had to reduce risks and send clear, positive signals to inbox providers.

Building a safe recovery segment

Cautiously, we did not restart sending to the full database. 

Instead, we built a very narrow segment that gave us the best chance of success, including:

• only highly engaged recipients;
• no recent bounces;
• clear history of opens and interactions.

We knew that our emails could still reach these were contacts who were also likely to engage. Everyone else was excluded at this stage.

Restarting sending from scratch

Performing domain recovery followed the same logic as warming up a brand-new domain:

• initial sends were limited to around 1,000 contacts;
• volume increased slowly and in small steps;
• no sudden jumps or experiments.

Although the domain had a long sending history, we treated it as an untrusted domain and started over.

What inbox providers needed to see

At this stage, content mattered less than behavior. Inbox providers needed several clear, repeatable signals:

• consistent engagement from recipients;
• low complaint and bounce rates;
• predictable sending patterns without spikes.

Only after these signals became stable did reputation begin to improve.

When and how we contacted the mailbox providers

After the abovementioned efforts, we did not contact the mailbox providers immediately. First, we needed proof that recovery was already in progress.

Why escalation happens later, not immediately

We waited until the following conditions were met:

• early recovery signals were visible in metrics;
• domain reputation improved by one level in Postmasters;
• delivery and bounce rates started to stabilize.

These indicated that our actions were working and that the issue was no longer ongoing.

What we shared with providers

When we reached out to Gmail and Microsoft, we explained the situation clearly by explaining:

• what caused the reputation drop;
• which steps were already completed;
• what we planned to do next.

The goal was not to ask for a quick fix but to show responsibility and transparency.

What changed after escalation

After conducting the provider review:

• bounce rates dropped further;
• inbox providers began accepting traffic more consistently;
• recovery speed improved, although the progress was still gradual.

Although direct contact did not replace warm-up discipline, it helped remove additional friction.

Returning to normal sending

Once trust signals improved, we started bringing back email programs carefully; nothing returned all at once.

What stayed restricted

Some activities remained off limits for a long time:

• reactivation and other low-engagement campaigns remained disabled;
• risky audience segments were excluded from sending.

This decision was made as these sends could undo weeks of recovery if reintroduced too early.

What was restored gradually

Other parts of the program came back step by step:

• triggered emails were moved back to the main domain;
• sending volume increased in controlled increments.

Each change was closely monitored before the next step.

How long before full recovery was achieved

From the first containment actions to full restoration, the process took up to three months. The new IP warm-up and domain recovery happened in parallel, helping shorten the overall timeline.

Before and after: key metrics

Notably, recovery became visible in metrics before reputation tools showed full green status.

Email performance metrics

• open rate: 25% → 11% → 36%;
• bounce rate and complaints: 1%-2% → around 20% → back to normal levels.

Once delivery stabilized, open rates not only recovered but exceeded the previous baseline.

Reputation signals

• full recovery was confirmed when Postmasters showed the highest reputation level;
• campaign metrics improved earlier and served as the first positive signal.

Both views were needed to confirm that real recovery was fully achieved and stable.

Business impact during recovery

Fixing deliverability came with a cost, as some losses were unavoidable during the recovery period.

What was affected

• manual promotional campaigns were unavailable for several months;
• triggered emails were heavily limited;
• email-driven traffic, registrations, and paid conversions declined.

Email could not operate at full capacity while trust was being rebuilt.

Why was the trade-off necessary

Accepting short-term losses prevented much larger damage at a later time. The priority was restoring sender trust and protecting long-term deliverability, not pushing volume while the domain was still fragile.

What we monitor now to prevent repeats

After recovery, we rebuilt our monitoring routine so that similar issues would be visible much earlier. The focus now is on signals that show loss of trust before delivery collapses.

Daily signals

Every day, we review a small set of core metrics, including the following:

• delivery rate;
• open rate;
• bounce rate.

These three metrics react first when something starts to go wrong. We do not wait for sharp drops; even small, consistent changes matter.

Weekly checks

Daily metrics alone are not enough. Reputation data move more slowly and require a separate review cycle. Thus, we take the following steps:

• Postmasters are checked twice a week;
• ESP alerts that notify us about unusual spikes in send volume are monitored.

We always factor in Postmaster reporting delays, which can be up to 3 days. That context is critical when comparing metrics with reputation status.

Thresholds we treat as warnings

Some signals now trigger immediate attention:

• any drop in IP or domain reputation, even by one level;
• early metric deviation from normal ranges.

We no longer wait for confirmation across multiple sources. One clear warning is enough to make us pause and investigate.

What we would do differently next time

Looking back, the biggest lessons were not about recovery but about preparation. Several decisions could have been made to reduce the risk long before the incident.

Infrastructure preparation

If we were starting again, we would change the setup earlier by:

• moving to dedicated IPs sooner;
• keeping multiple warmed subdomains ready;
• maintaining backup domains for emergency switches.

These steps reduce dependency on external factors and give more control during incidents.

Sending strategy

As sending discipline matters just as much as infrastructure, always:

• keep critical triggers on subdomains by default;
• avoid sharp increases in send volume;
• treat any reputation dip as urgent and act immediately.

Small delays in response can turn manageable issues into long recovery cycles.

Key takeaways

1. Delivery collapsed due to sending behavior, not email content.
2. Early detection through Postmasters prevented a full shutdown.
3. Pausing promotions and isolating critical triggers limited business damage.
4. Dedicated IPs removed dependency on a shared reputation.
5. Domain trust was rebuilt through slow, engagement-only sending.
6. Provider escalation helped once recovery signals became visible.
7. Full recovery required patience, discipline, and strict volume control.

Wrapping up

Email deliverability problems rarely have a single cause or a quick fix. In our case, recovery meant stopping risky sends, changing infrastructure, and rebuilding trust from the ground up. The process was slow and costly, but it protected the sender’s long-term reputation and restored stable inbox placement.

The biggest lesson here is simple: preventing reputation loss is easier than fixing it. Regular monitoring, careful volume control, and prepared fallback options make the difference when something goes wrong.