Fardeen KarimReply rates fall off a cliff, test emails land in spam, and warm-up inbox rates drop. The domain is in trouble. Most sending domains can be brought back if you stop quickly and work through the causes in order. This is the process I use, and when I decide a domain isn't worth saving.
The short version: stop campaigns on the domain (keep warm-up running), fix authentication, check blocklists, find what changed, let warm-up rebuild it for one to two weeks, then return at a third of the old volume and ramp up slowly.
How to tell a domain is in trouble
- Replies drop sharply across every campaign that uses the domain, while other domains hold up.
- Warm-up inbox rates fall and spam rates climb for its mailboxes.
- An inbox placement test lands in spam at Gmail or Outlook.
- Bounces or "try again later" responses rise.
- The domain appears on a blocklist.
Step 1: stop campaign sending on that domain
Pause every campaign mailbox on the domain. Every extra email sent while it's in trouble digs the hole deeper. Keep warm-up running: the positive signals it creates are what bring the domain back.
Step 2: check authentication
Run the domain health checker. The usual suspects:
- DKIM stopped signing, often after a change at the mail provider.
- A second SPF record added by a new tool, which breaks SPF for everything.
- DMARC missing, or set to reject while SPF or DKIM is broken.
- The MX record removed or changed, so replies and bounces don't arrive.
Fix anything red first, then send a test to a Gmail address you own and paste its headers into the email header analyzer to confirm SPF, DKIM and DMARC all pass.
Step 3: check blocklists
Run the blacklist checker. If the domain or its sending IP is listed, note which lists, and don't request removal until the cause is fixed: lists re-add senders who keep doing the same thing.
Step 4: find the cause
Look at what changed in the days before the drop:
- A new list with high bounces: the most common cause in my experience. Check its bounce rate.
- A volume jump: new campaigns pushing mailboxes past a safe daily number.
- Link tracking switched on, or a new link in the email to a domain with a poor reputation.
- Complaints: an offer or audience that annoyed people.
- A shortened warm-up: new mailboxes sent campaigns before they were ready.
Step 5: rest and recover
With the cause fixed, let warm-up run on its own for one to two weeks. Watch the warm-up inbox rate climb back day by day.
When to retire a domain instead
If the inbox rate doesn't move after two weeks of rest, or the domain sits on a major blocklist that won't remove it, it's cheaper to retire it and warm a new one than to keep fighting. Keep the old domain's website redirect running; just stop sending from it.
Step 6: return slowly
Bring campaigns back at about a third of the old volume, with a freshly verified list, no link tracking and plain emails. Raise volume over two weeks while watching bounces and placement. Request blocklist removal once the domain has been clean for a while.
Prevent it next time
- Verify every list right before it's used.
- Keep every mailbox at a steady, modest daily volume: around 30 cold emails a day.
- Check every domain's health and blocklists on a schedule.
- Keep a few warmed spare domains, so a resting domain doesn't stop your campaigns.
- Never send cold email from your main domain, so a domain in trouble is one you can rest.
Questions people ask
Can a domain reputation be reset?
Not directly: providers don't offer a reset. Reputation recovers as good signals replace bad ones, which is what the rest-and-return steps do.
Should I delete the mailboxes and start again on the same domain?
No. The reputation belongs mostly to the domain, so new mailboxes on it inherit the problem. Fix the cause, or move to a new domain.
mailzy watches every sending domain's records and blocklists, shows each mailbox's inbox and spam rates, gives every domain a reputation label, rests mailboxes whose health drops, and pauses a campaign by itself if its bounces climb too high. See deliverability.