Why are my cold emails going to spam?

Common causes include missing or broken SPF, DKIM, or DMARC records, sending too much from new or unwarmed mailboxes, high bounce rates from unverified lists, spam complaints from poorly targeted recipients, and content with many links or images. Check authentication, volume, list quality, and complaint data first.

How many cold emails can I send per day per mailbox?

There is no official limit that guarantees inbox placement. Many teams keep cold volume per mailbox modest and spread larger campaigns across several warmed mailboxes. New mailboxes should start much lower and ramp gradually. Watch complaint and bounce rates rather than relying on a fixed number.

Should I use a separate domain for cold email?

Many teams do, to protect their primary domain's reputation for customer and transactional mail. A secondary domain still needs proper authentication, warmup, and responsible sending. Make sure recipients can clearly identify who you are, and keep cold, warm, and bulk mail in separate lanes.

Cold Email Deliverability Best Practices

Cold email deliverability is the ability of your outreach to reach recipients' inboxes rather than spam folders. Best practices include authenticating domains with SPF, DKIM, and DMARC, warming up new mailboxes, verifying addresses, keeping daily volumes per mailbox modest, separating cold mail from customer mail, writing plain relevant messages, offering easy opt-outs, and monitoring bounce and complaint rates.

Why deliverability matters

If cold emails land in spam, nothing else matters: not the targeting, the copy, or the offer. Inbox providers decide placement using sender reputation, authentication, recipient engagement, and content signals. Cold email is especially vulnerable because recipients do not expect it and may mark it as spam, which damages reputation for every future message from that sender.

Authenticate your domains

Set up SPF to list the servers allowed to send for your domain, DKIM to sign messages cryptographically, and DMARC to tell providers how to handle mail that fails checks and send you reports. Google and Yahoo introduced stricter requirements for bulk senders in 2024, including authentication, easy unsubscribe for marketing mail, and low spam complaint rates. Even if your volume is below bulk thresholds, meeting these standards improves placement.

Use separate domains and mailboxes for cold outreach

Many teams send cold email from secondary domains that resemble their main brand, keeping the primary domain for customer and transactional mail. Separate lanes for cold outreach, mail to people who signed up, and broadcasts to opt-in lists mean a problem in one lane does not damage the others. Replies should stay in the lane where the conversation started.

Warm up and ramp slowly

New mailboxes and domains need warmup: low daily volume at first, increasing gradually over weeks. Keep per-mailbox volume modest even after warmup and spread larger campaigns across several warmed mailboxes. When a mailbox reaches its daily cap, let mail wait rather than switching senders mid-thread.

Keep lists clean

Verify addresses before sending to avoid hard bounces, remove role addresses where appropriate, and never buy unverified bulk lists. Check every address against a permanent suppression list of unsubscribes, complaints, and hard bounces. Targeting matters for deliverability too: relevant messages get fewer complaints and more replies, which strengthens reputation.

Write deliverable messages

Plain, short, personal messages tend to perform better than heavily designed emails. Avoid excessive links, large images, attachments in first messages, misleading subject lines, and spam-triggering phrasing. Include the sender's real identity, a postal address where required, and a clear way to opt out. Tracking pixels and link tracking can affect deliverability; some teams minimise them for cold outreach.

Honour opt-outs instantly and permanently

Make opting out easy, through a one-click link or a simple reply, and act on it immediately. Suppressed addresses should never be contacted again by anyone on the team, including AI agents and external reps. Ignoring opt-outs causes complaints, legal risk, and reputation damage.

Monitor health and pause automatically

Track bounce rates, spam complaint rates, reply rates, and inbox placement per mailbox and domain. Google's guidance asks senders to keep reported spam rates low and avoid reaching 0.3 percent. Set automatic pauses: Koryo, for example, pauses a mailbox or domain and alerts the team when its seven-day complaint rate passes 0.3 percent or its hard-bounce rate passes 5 percent after twenty sends, with both thresholds configurable.

Diagnose problems quickly

If replies drop or placement tests show spam folder delivery, check authentication records, recent changes in volume or content, list sources, blocklist status, and complaint data. Pause sending from affected mailboxes, fix the cause, and resume slowly. Recovering a damaged domain takes much longer than protecting a healthy one.

Deliverability for AI agents and external reps

When AI agents or independent reps send on your behalf, their messages affect the same domain reputation as your team's. Give them warmed mailboxes in the cold lane, apply daily caps, and route every message through the same suppression, consent, and capacity checks. One operator sending carelessly can damage deliverability for everyone sharing the domain.

A deliverability checklist

Before each campaign, confirm authentication records pass, mailboxes are warmed and below their caps, the list is verified and checked against suppression, messages are plain and relevant with a clear opt-out, and monitoring with automatic pauses is active. Review results within the first day and pause if complaints or bounces spike.

Testing inbox placement

Send test messages to seed accounts across major providers before a campaign and periodically during it. Placement tests reveal spam or promotions folder delivery early, before poor results show up in reply rates.

Keep records

Keep a log of changes to domains, mailboxes, volumes, and lists. When deliverability shifts, a clear history makes the cause much easier to find.

Frequently asked questions

Why are my cold emails going to spam?: Common causes include missing or broken SPF, DKIM, or DMARC records, sending too much from new or unwarmed mailboxes, high bounce rates from unverified lists, spam complaints from poorly targeted recipients, and content with many links or images. Check authentication, volume, list quality, and complaint data first.
How many cold emails can I send per day per mailbox?: There is no official limit that guarantees inbox placement. Many teams keep cold volume per mailbox modest and spread larger campaigns across several warmed mailboxes. New mailboxes should start much lower and ramp gradually. Watch complaint and bounce rates rather than relying on a fixed number.
Should I use a separate domain for cold email?: Many teams do, to protect their primary domain's reputation for customer and transactional mail. A secondary domain still needs proper authentication, warmup, and responsible sending. Make sure recipients can clearly identify who you are, and keep cold, warm, and bulk mail in separate lanes.