Most cold email problems are not copy problems. They are deliverability problems that look like copy problems, because an email that lands in spam gets the same zero replies as a bad one.
This is the checklist we would hand a founder or a small sales team before their first campaign. It is grouped by stage, with a copyable version at the end.
Before you send
Authentication (SPF, DKIM, DMARC)
- SPF lists which servers can send for your domain. One SPF record per domain, no duplicates.
- DKIM signs your messages so the receiving server can verify they were not altered. Turn it on in Google Workspace or Microsoft 365 and publish the key.
- DMARC tells receivers what to do when SPF or DKIM fail. A common starting point is
p=nonewith a reporting address, then tighten later once you know everything legitimate passes.
Check that all three pass on a real test message, not just that the records exist.
Separate sending domains
Do not send cold email from your main company domain. If a campaign goes badly, you want the damage to land on a secondary domain, not the one your invoices and customer support run on.
A common pattern is a few lookalike domains (for example getacme.com or tryacme.com) that redirect to your main site, each with 2 to 3 inboxes. We cover the details in setting up domains and inboxes for cold email.
Warmup
New inboxes have no sending history. Warmup builds some by exchanging normal-looking emails with other inboxes that open and reply to them.
A common rule of thumb is two to three weeks of warmup before any cold sends, and keeping warmup running in the background after you start.
List verification
Verify every list before it goes into a sequence. Remove invalid addresses, and be careful with catch-all domains (servers that accept any address, so you cannot confirm the person exists).
Your copy
- Plain text first. Cold email should look like an email from a person. Skip HTML templates, banners, and heavy formatting.
- One link at most, ideally none in the first email. Links (especially link shorteners and tracking-heavy URLs) add risk. Many teams leave links out of step one entirely and add them in follow-ups.
- No images or attachments in the first touch. They add weight and trigger more scrutiny.
- Watch the spammy phrasing. Lines like "100% free", "act now", "guaranteed", and all-caps subject lines read like spam to filters and to people.
- Personalize for real. A first name variable is not personalization. One specific line about the company, role, or a recent event does more for replies and for engagement signals than any template trick.
- Vary your wording. Sending thousands of identical emails creates a recognizable fingerprint. Spintax and a few rotated variants help, as long as every variant still reads naturally.
- Make opting out easy. A simple line like "Not relevant? Just reply and I won't follow up" lowers complaints.
While sending
Daily caps per inbox
A commonly cited range is 30 to 50 cold emails per inbox per day. If you need more volume, add inboxes and domains rather than pushing one inbox harder.
Ramp slowly
Do not go from zero to your full cap on day one. A common approach is to start new inboxes at 10 to 20 cold sends a day and add a handful each few days while you watch bounces and replies.
Rotate across inboxes
Spread each campaign across several inboxes so no single sender carries the whole load. If one inbox has a problem, the rest of the campaign keeps running.
In SuperSend, cold email sequences rotate across all the inboxes you connect, so you set the caps once and the volume spreads itself.
Send windows
Send during your prospect's working hours, in their time zone, with some randomness between messages. And make sure every sequence stops the moment someone replies.
Monitoring
Check these weekly at minimum, daily during a ramp.
| Signal | Rule of thumb | What it tells you |
|---|---|---|
| Hard bounce rate | Keep under ~2% | List quality. Above this, stop and re-verify. |
| Spam complaint rate | Aim under 0.1%, stay well clear of 0.3% | How recipients feel about your emails. |
| Reply rate | Watch the trend, not one number | A sudden drop often means placement changed. |
| Inbox placement test | Mostly inbox at Gmail and Outlook | Where your emails actually land. |
| Authentication | SPF, DKIM, DMARC all passing | Whether a DNS change broke something. |
These are rules of thumb, not guarantees. Your own baseline matters more than any industry number.
Know the Gmail and Yahoo rules
Since 2024, Gmail and Yahoo have enforced stricter requirements for bulk senders (Google defines this as sending around 5,000 or more messages a day to Gmail addresses). The short version:
- Authenticate with SPF and DKIM, and publish a DMARC record.
- Make unsubscribing easy. For marketing and subscribed mail this means one-click unsubscribe. For cold email, a clear way to opt out is the minimum.
- Keep spam complaints low. Google recommends staying under 0.1% and never reaching 0.3%, which is the commonly cited ceiling.
Even below the bulk threshold, these rules describe what mailbox providers reward, so treat them as your baseline.
Run placement tests
Bounce and complaint rates tell you about problems after the fact. A placement test sends a copy of your email to seed inboxes and shows whether it hit the inbox, promotions, or spam.
Run one before a new campaign and any time replies drop without explanation. SuperSend's deliverability tools include placement tests (they use plan credits, 5 credits per seed) alongside sender health and bounce monitoring.
When things go wrong
Replies drop, bounces spike, or a placement test comes back mostly spam. Here is the order to work through.
- Check authentication. Send a test and confirm SPF, DKIM, and DMARC all pass in the headers.
- Isolate the sender. Look at results per inbox and per domain. If one sender is the problem, the fix is local.
- Check the list. A bounce spike usually traces back to one list or one data source. Re-verify it.
- Check the copy. Did you add a link, an image, or new wording right before the drop? Revert and test again.
- Run a placement test on a plain-text version to separate content problems from sender reputation problems.
When to pause
Pause a campaign when hard bounces climb above about 2%, or complaints start showing up. Fix the list or copy before resuming.
Pause a sender when one inbox or domain consistently lands in spam while others on the same campaign do fine. Keep warmup running, drop it out of rotation, and bring it back slowly once placement recovers.
Pausing for a week costs you less than burning a domain.
The copyable checklist
## Before you send
- [ ] SPF, DKIM, and DMARC set up and passing on a real test email
- [ ] Sending from secondary domains, not the main company domain
- [ ] 2 to 3 inboxes per sending domain
- [ ] Inboxes warmed for 2 to 3 weeks, warmup left running
- [ ] Every list verified, catch-alls handled carefully
## Your copy
- [ ] Plain text, no HTML templates
- [ ] No links (or one) in the first email
- [ ] No images or attachments in the first touch
- [ ] No spammy phrases or all-caps subject lines
- [ ] At least one real personalized line per email
- [ ] Variants or spintax so emails are not identical
- [ ] Easy, clear way to opt out
## While sending
- [ ] Daily cap per inbox set (common range: 30 to 50)
- [ ] New inboxes ramped from 10 to 20 per day
- [ ] Campaign rotating across multiple inboxes
- [ ] Send windows set to prospect time zones
- [ ] Sequence stops on reply
## Monitoring
- [ ] Hard bounces under ~2%
- [ ] Spam complaints under 0.1%, never near 0.3%
- [ ] Reply rate tracked weekly against your own baseline
- [ ] Placement test before each new campaign
- [ ] Authentication rechecked after any DNS change
## When things go wrong
- [ ] Authentication checked first
- [ ] Problem isolated by inbox and domain
- [ ] List re-verified
- [ ] Recent copy changes reverted and retested
- [ ] Campaign or sender paused until fixed
The short version
- Authenticate every sending domain with SPF, DKIM, and DMARC, and keep cold email off your main domain.
- Warm up new inboxes, verify every list, and ramp volume slowly.
- Write plain, personal emails with few or no links and an easy way to opt out.
- Keep hard bounces under about 2% and spam complaints well under 0.3%.
- When results drop, check authentication, isolate the sender, fix the list, and pause before you burn a domain.
Warmup, DNS checks, and bounce monitoring come with every SuperSend plan. See pricing.
