When deliverability drops, the instinct is to rewrite your email. That is almost always the last thing that matters. The fixes have an order, from fastest and most common to slowest, and working them out of order costs you days.
This is the exact sequence I run through. Start at step one and only move on once each step is clean.
First, confirm you actually have a problem
Open rate dropping is not proof of a deliverability problem. Open tracking is unreliable, blocked or pre-fetched by many clients. Before you change anything, get a real measurement.
Run an inbox placement test from the affected mailbox. If you are landing in primary, your problem is targeting or copy, not deliverability. If you are landing in spam or not delivered, continue down this list.
Step 1: Check your authentication
This is the most common cause and the fastest fix, so it goes first. Broken or missing SPF, DKIM, or DMARC tells mailbox providers you are unverified, and in 2026 that alone can route you to spam.
Run your sending domain through the free SPF, DKIM and DMARC checker. All three should pass. A common silent failure is an SPF record that broke when you added a new sending tool, or a DKIM key that was never published. Fix any failure before touching anything else. The authentication guide covers each record.
Step 2: Check blacklists
If authentication is clean, check whether your domain or IP got listed. A blacklist listing can tank placement overnight, and it often happens without any obvious cause on your end, especially on shared infrastructure.
Run your domain and sending IP through a blacklist checker. If you are listed, find the delisting process for that specific blacklist, fix the underlying cause first, then submit the request. Delisting without fixing the cause just gets you relisted.
Step 3: Audit your list quality
A high bounce rate is a spammer signal, and it compounds fast. If your last campaign bounced above 3 percent, your list is the problem and it is actively damaging your reputation with every send.
Stop sending to that list. Run it through an email verifier, cut every invalid and risky address, and only resume with the clean remainder. Going forward, validate on import so a bad list never reaches your campaigns. SendKit does this automatically. The bounce rate guide covers the full picture, including the secure email gateways that bounce valid addresses.
Step 4: Review your volume and ramp
Sending too much, too fast, from a domain that has not earned it is a classic self-inflicted wound. If you recently doubled volume or added new mailboxes and skipped warmup, that is likely your cause.
Pull volume back to a conservative level per mailbox and hold it there. New mailboxes need a warmup ramp before they carry real campaigns. Spreading volume across more mailboxes at a lower per-mailbox rate is almost always safer than pushing a few mailboxes hard.
Step 5: Fix obvious content problems
Now content. Not because it never matters, but because it rarely matters until the first four steps are clean. Run your template through the free spam checker and cut the obvious triggers: spammy phrases, heavy links, large images, shouting formatting.
Keep cold emails short and plain. A three-line text email from a clean setup outperforms a polished HTML email from a broken one, every time.
Step 6: Rebuild reputation
If reputation is already damaged, the fixes above stop the bleeding but do not heal it. Healing happens through controlled, low-volume sending that generates positive engagement over time.
Pull the affected mailboxes out of active campaigns and run warmup on them to rebuild engagement signals. Re-enable them only when health metrics recover. With SendKit you can watch per-mailbox reply and bounce rate to know when a mailbox is safe to send from again.
How long recovery takes
Set expectations honestly. Authentication and list fixes are immediate. Blacklist delisting takes 24 to 72 hours once the cause is fixed. Reputation rebuilding takes two to four weeks of careful sending. There is no button that resets a burned domain.
The faster path is not to get here in the first place: solid infrastructure, real authentication, validated lists, and a proper warmup ramp. If you are rebuilding from scratch anyway, it is worth fixing the foundation so you are not back here in a month.