A cold email that lands in spam does not exist. Deliverability is the foundation of every cold email program, and most problems come from a handful of setup mistakes that are easy to avoid.
This guide walks through the setup we use before a single prospect is contacted.
How mailbox providers decide where email goes
Providers such as Google and Microsoft look at many signals to decide whether an email reaches the inbox. The main ones are who you are, whether you are authenticated, how your domain and sending servers have behaved in the past, and how recipients react to your email.
Positive reactions, such as replies, and negative ones, such as spam reports, bounces and deletions without reading, all shape your reputation over time. Good deliverability is the result of consistent, careful sending rather than a single trick.
1. Never send cold email from your main domain
Your main domain carries your everyday email: sales conversations, invoices, support. If cold outreach damages its reputation, all of that suffers. Instead, register secondary domains that are close variations of your brand and redirect them to your main website.
Spreading volume across several domains and mailboxes also limits the impact if one runs into problems.
2. Authenticate every sending domain
Mailbox providers check whether you are allowed to send from a domain. Set up three records on every sending domain:
- SPF: lists the services allowed to send email for the domain
- DKIM: signs each email so the receiver can verify it was not altered
- DMARC: tells receivers what to do with email that fails the checks, and sends you reports
Major mailbox providers now expect authentication from bulk senders, and missing records are one of the most common reasons outreach goes to spam.
Check your records
After setting up SPF, DKIM and DMARC, test them. Free tools from your email provider and third parties can confirm the records are valid and aligned. Start DMARC with a monitoring policy, review the reports, then tighten it once you are confident legitimate email passes.
Also check that each sending domain has a simple website or redirect, a custom tracking domain if you use link tracking, and consistent sender names.
3. Warm up new mailboxes
A brand-new mailbox that suddenly sends hundreds of emails looks suspicious. Warm up each mailbox gradually over several weeks, increasing volume slowly and building a history of normal sending and engagement before starting campaigns.
4. Verify every list before sending
Bounces are one of the strongest negative signals for deliverability. Verify every email address before it enters a sequence, remove role addresses where they are not useful, and never buy generic lists. Good data starts with a clear ICP built from closed-won deals and careful lead generation.
5. Keep volume per mailbox modest
High volume from a single mailbox raises risk. Keep daily sends per mailbox conservative and scale by adding mailboxes and domains rather than pushing one inbox harder. Sending in smaller, well-targeted batches is safer and usually performs better.
6. Write emails that look like real emails
- Plain text, with few or no links and no images in the first email
- Short messages written for one person, not a broadcast
- Clear identification of who you are and an easy way to opt out
- Personalisation that reflects real context, not just a first name
Relevance protects deliverability too. When recipients reply instead of ignoring or reporting your email, mailbox providers treat your domain more favourably.
Follow the rules for bulk and cold senders
Major mailbox providers have tightened their requirements for senders in recent years, including authentication, easy unsubscribes and low spam complaint rates. Read the current sender guidelines from Google and Microsoft and treat them as the minimum standard, not the target.
Legal rules for cold email also vary by country. In many regions B2B outreach is allowed when it is relevant to the recipient's role, identifies the sender and offers a simple opt-out. Check the rules for every region you target and honour opt-outs immediately.
Signs your deliverability is slipping
- Open or reply rates drop suddenly across several campaigns
- Bounce rates rise above what you normally see
- Test emails land in spam or promotions
- Replies mention that your email was in their junk folder
- Your provider's reputation tools show a decline
When you see these signs, slow down. Pause the affected domains, check authentication and lists, reduce volume and review your copy for spam triggers such as heavy links or aggressive language.
7. Monitor and adjust weekly
Watch bounce rates, spam complaints, reply rates and inbox placement for every domain. If a domain shows problems, pause it, investigate and let it recover. Rotate content, review lists and keep authentication records healthy.
Managing replies and opt-outs
Replies affect deliverability as well as pipeline. Respond quickly to positive and neutral replies, and handle opt-outs immediately and permanently. Keep a single suppression list that every sending tool and mailbox checks, so someone who opted out from one domain never hears from another.
Auto-replies, bounces and out-of-office messages also need handling. Remove hard bounces from every list, pause contacts who are away and note role changes from replies so your data stays accurate. Most cold email platforms can categorise replies automatically, but a person should still review anything that looks like interest.
Positive replies should move into your CRM straight away with the full conversation attached, so whoever books the meeting has context. That is where appointment setting takes over.
Test inbox placement
Do not assume your email reaches the inbox because it did not bounce. Send test emails to accounts you control across major providers, such as Gmail and Outlook, and check whether they land in the inbox, promotions or spam. Many cold email and deliverability tools include placement tests that do this automatically.
Test before launching a new campaign, after changing copy significantly and whenever performance drops. Placement often differs between providers, so a campaign that works well for Gmail recipients may struggle with Outlook, or the reverse.
Choosing a sending platform
Cold email platforms such as lemlist and Instantly handle sequencing, mailbox rotation, warm-up and reply detection. When comparing them, look at:
- How well they spread sending across many mailboxes
- Whether warm-up and deliverability monitoring are built in
- How replies are detected, categorised and synced to your CRM
- Support for multichannel steps such as LinkedIn tasks
- Who owns the data and how easy it is to export
The platform matters less than the setup behind it. A well-configured mailbox on any reputable tool performs better than a poorly configured one on the most expensive tool.
Writing sequences that protect deliverability
A good cold sequence is short and spaced out. Three or four emails over two to three weeks is usually enough. Each follow-up should add something new, such as a relevant example, a different angle or a useful resource, rather than "just bumping this to the top of your inbox".
- Keep the first email under about 100 words
- Avoid attachments and multiple links, especially early in the sequence
- Vary wording across prospects instead of sending identical text
- Stop the sequence immediately when someone replies, in any channel
What to do when a domain is damaged
If a sending domain shows serious problems, stop sending from it. Check whether the cause was a bad list, a sudden volume increase or a copy issue, and fix that first. Some domains recover after a rest period and slow warm-up. Others are better retired and replaced. Because your main domain was never used for cold email, a damaged secondary domain is an inconvenience, not a crisis.
Combine email with other channels
Cold email works better alongside LinkedIn outreach, where prospects can see a real person behind the message. And whether you run it in-house or with a partner, the same setup applies, which we compare in in-house SDRs vs an outbound agency.
If you want this infrastructure set up and managed, our cold email service handles domains, authentication, warm-up and monitoring for you.
Deliverability checklist
- Use secondary domains, never your main domain
- Set up SPF, DKIM and DMARC on every sending domain
- Warm up every new mailbox gradually
- Verify every address before it enters a sequence
- Keep daily volume per mailbox conservative
- Write short, plain, relevant emails with a clear opt-out
- Monitor bounces, complaints and placement weekly
- Pause and investigate at the first sign of problems