Apollo Email Deliverability Guide: Warmup and Troubleshooting

Apollo is a sequencing tool, not a deliverability system.

It sends emails, but it does not manage where those emails land, Gmail and Outlook do. Most Apollo users assume the platform is influencing inbox placement, but mailbox providers make that decision based on sender reputation, email content, and sending setup.

Because Apollo doesn’t monitor any of those signals, teams often start sending before the domain is warmed, authenticated, or trusted. When that happens, outreach performance becomes inconsistent, even when the messaging is strong.

This guide focuses on the part Apollo cannot control: building a sending environment that mailbox providers trust. You’ll learn how to authenticate your domain correctly, warm up your inboxes the right way, and monitor the signals that actually determine inbox placement.

Understanding Why Apollo Emails Land in Spam

Before diving into the causes, it’s important to understand one thing: Apollo has no visibility into how Gmail and Outlook score your domain. The platform shows opens, replies, and sequence performance, but deliverability decisions happen entirely inside mailbox providers.

That means authentication failures, reputation drops, throttling, and placement shifts can all be happening behind the scenes while Apollo still shows “emails sent.”

Here are the real triggers behind Apollo emails landing in spam—issues Apollo cannot detect or prevent:

1. Weak or missing authentication

Most email providers verify each message using three email authentication standards:

• SPF (Sender Policy Framework)
• DKIM (DomainKeys Identified Mail)
• DMARC (Domain-based Message Authentication, Reporting, and Conformance)

When these records are absent or misconfigured, Apollo will still “send,” but providers may send your emails straight to spam. Apollo does not monitor alignment or DNS errors, MailReach does.

2. Poor sender reputation

Mailbox providers evaluate how recipients interact with your emails. Low opens, low replies, quick deletions, and no positive engagement reduce your reputation over time.

That reputation is one of the primary signals Gmail and Outlook use to decide whether your next message reaches the inbox or the spam folder.

Apollo reports engagement inside your sequence, but mailbox providers maintain their own engagement records. Their data drives inbox placement. When that data shows weak or declining interaction, your reputation drops and visibility decreases.

3. Email content

Filters evaluate the entire composition of an email. They analyze the HTML structure, text-to-code ratio, link behavior, embedded elements, tracking patterns, and formatting anomalies. A message can be flagged even when it contains a single link to a legitimate website.

4. Sudden sending activity

If a new domain jumps from 0 to 200 sends overnight, Gmail/Outlook treat it as suspicious. Apollo will let you schedule it; providers will throttle it or filter it. MailReach identifies this pattern early so you can adjust before reputation drops.

To learn more, read our guide on how to prevent emails going to spam.

Step-by-Step Apollo Setup Guide for Improved Deliverability

Good deliverability starts before you hit “Send.” The steps below ensure your technical setup is correct from day one:

1. Configure your domain for authentication

Mailbox providers don’t trust Apollo’s sends by default. They trust your domain’s authentication. Make sure these three records are correctly added and aligned before sending anything.

1. SPF: Allows Gmail/Outlook to confirm your sending server is authorized.
   Keep a single SPF record, stay within lookup limits, and use the right qualifier (~all or -all).
2. DKIM: Signs your emails so providers can verify they weren’t modified.
   Use a unique selector for Apollo to avoid overwriting DKIM from other tools.
3. DMARC: Tells providers what to do when SPF or DKIM fail.
   Start with p=none to monitor alignment, then tighten once everything is passing consistently.

Check DNS Alignment and Propagation for Apollo

Apollo doesn’t manage DNS or reputation settings. Those are controlled by your domain host, so authentication records that establish your domain’s credibility must be configured at your DNS provider. To do this:

• Log in to your DNS dashboard
• Add the SPF, DKIM, and DMARC records generated by Apollo or your mailbox provider
• After updating DNS, verify that each record resolves correctly

Use MailReach’s SPF Checker to confirm the SPF record is published, formatted correctly, and authorizes the designated sending servers. It also flags lookup-limit or duplicate-record issues that can break SPF validation when your Apollo campaigns go live.

Then use MailReach’s DKIM Checker to confirm your selector is visible, the DKIM record is publicly reachable, and the key is configured with an appropriate length. It will also alert you to problematic selector names or key lengths that could cause delivery failures.

2. Add a custom tracking domain and verify the setup

When multiple senders share the same tracking domain or the same SMTP (Simple Mail Transfer Protocol) path, their reputations become linked. If one user’s links are reported or blocked, the entire pool inherits part of that negative reputation.

That means your emails could be routed to spam, even if your campaigns follow best practices. For example, if Apollo’s shared tracking domain is “apollo-track.com,” your links might appear as “https://apollo-track.com/c/abc123”

Mailbox filters treat this as bulk infrastructure used by unrelated senders.

Therefore, to isolate your reputation, do the following:

• Create a custom tracking subdomain, such as link.yourdomain.com or track.yourdomain.com
• Point this tracking subdomain’s CNAME record to Apollo’s tracking endpoint

Test the new setup using MailReach’s email spam tester. The test sends your email to over 30 real inboxes and shows exactly where it lands (Inbox, Promotions, or Spam) across major mailbox providers.

The tool also displays the full message content and link URLs, enabling you to verify that your tracking URLs now use your custom subdomain instead of Apollo’s shared tracker.

Warming Up Your Apollo Mailboxes the Right Way

Apollo helps you send emails, but it doesn’t warm up your inboxes. Warming up inboxes is your responsibility. Here’s how to do it effectively:

1. Start with a controlled ramp-up

New domains need time to earn trust. Mailbox providers monitor your ramp-up behavior. Begin small, sending around 3 to 5 emails per day during the first week.

Stick to a 3–4-week ramp-up so filters have time to learn from engagement patterns and for volume to stabilize. You can use the ramp-up schedule below as a reference.

If open or reply rates drop, pause any increases and keep your daily volume steady until engagement recovers.

After completing your first month of steady warm-up, adding additional weeks won’t significantly improve Apollo email deliverability. By that point, most providers will have already established a trust profile for your domain.

The upper safe limit for Google Workspace and Office 365 inboxes is approximately 100 emails per day per mailbox. Once your manual warm-up pattern stabilizes, extend the process through automation.

MailReach conducts its warm-up across a network of 30,000+ verified Google Workspace and Office 365 inboxes, where each open, reply, and mark emails as important , all actions happening in real user environments.

2. Focus on engagement

Email warm-up only works when your messages sound human. Filters quickly detect e identical templates, fixed wording, and mechanical timing.

Use an email warmup tool that has a direct impact on the signals Gmail and Outlook record.

Warmers built on real Workspace and Office365 inboxes generate safer, more credible interactions than tools that rely on low-quality or artificial accounts.

A high-quality warmer will:

• Vary tone, structure, and length across messages
• Generate realistic opens, replies, and positive interactions
• Remove messages from spam automatically
• Spread warm-up across many trusted inboxes

These actions improve your early credibility and stabilize placement before you start sending Apollo sequences.

In addition, keep your initial templates short and simple while warming. Limit links, images, and formatting. This reduces the chance of content-level filtering while your reputation is strengthening.

Troubleshooting Apollo Email Deliverability Issues

Mailbox filters adapt to any changes in engagement and can trigger new spam behavior patterns. When that happens, here’s what you need to do to reset your approach methodically:

1. Stop sending emails temporarily

Temporarily suspend Apollo sends for 48–72 hours. Sending during a decline increases the negative reputation signals mailbox providers rely on to authenticate and filter messages. Pausing your campaign gives you the time to identify the problem and fix it.

2. Identify the root cause

Determine why performance declined before taking corrective action. Look for early indicators such as:

• Open rates falling below ~15%
• Reply rates dipping under ~2%
• A rise in soft bounces or deferrals
• Consistent placement in Promotions or Spam folders

Use diagnostics outside Apollo to pinpoint the failure:

• Google Postmaster Tools to check for sharp declines in domain reputation
• DMARC reports to check for SPF or DKIM misalignment issues
• Public blocklists to check for domain or IP flags

3. Correct the underlying problem

Once the cause is clear, apply the appropriate fix. The table below maps common scenarios to targeted solutions. The key is to make recovery intentional rather than reactive:

4. Rebuild sender reputation

After addressing the issue, resume sending emails with a gradual warm-up instead of jumping back to full scale. A 7–14 day recovery window is typical for minor problems. For deeper reputation damage (e.g., blocklisting, repeated low engagement), recovery may take 28–35 days.

Apollo Email Deliverability Best Practices for Long-Term Optimization

After your domain and mailboxes are properly warmed, the priority becomes maintaining the trust signals you’ve built.

1. Maintain regular list health

List quality directly influences your sender reputation. Even authenticated, well-warmed domains degrade if they continue sending to inactive or invalid addresses. 

Therefore, use an email verifier to remove invalid or risky contacts before adding them to Apollo. This reduces bounces and stabilizes your reputation across Gmail and Outlook.

A smaller, high-quality list consistently performs better and protects long-term deliverability.

2. Continuously track deliverability metrics

Engagement data tells only part of the story. To maintain Apollo email deliverability, monitor inbox placement and domain health regularly. Here’s a reference table you can include in your dashboard:

When any of these metrics slip for more than 7–10 days, pause and diagnose before continuing to improve email deliverability.

How MailReach, a Dedicated Deliverability Platform, Helps Sustain Inbox Placement Over Time

Once your Apollo setup, warm-up, and sending cadence are in place, the real challenge is maintaining consistent deliverability.

Reputation shifts gradually, sometimes over days, sometimes across campaigns, and those changes aren’t always visible from within Apollo.

That’s where MailReach provides continuity, bridging gaps that Apollo alone can’t detect. It runs automated email warm-ups in the background, monitors inbox placement across providers, alerts you when authentication, engagement, or reputation begins to drift.

Instead of waiting for a decline to appear in your campaign results, you can act on early indicators and correct issues before inbox placement drops.

Give your emails a first class ticket to the inbox with MailReach’s email warmup tool. Improve your Apollo email deliverability.