High bounce rates from Apollo? Here's how to protect your domain.

If you send outbound email from Apollo.io and your messages started landing in spam, you're not imagining it. Many users describe the same thing: open rates that drop, bounce rates that spike, and a domain that suddenly stops reaching people.

There are two causes worth understanding. One is how the email is sent. The other is the contact data you send to.

Shared sending means shared reputation

Gmail and Microsoft don't judge each email on its own. They look at patterns across groups of senders: the IP addresses, the headers, and the way mail goes out.

When many senders share the same sending setup, they share its reputation too. Some call this "herd liability". One careless sender in the group can pull the reputation down for everyone in it.

Apollo users report exactly this: open rates falling suddenly, with no warning. Many point to shared headers and sending patterns that spam filters can spot easily.

Old contacts, high bounces

The second problem is the data. Contact details go out of date. People change jobs, companies close, inboxes get deleted. A contact can still be marked "verified" long after the address stopped working.

Some users report hard bounce rates as high as 45% on Apollo contacts marked "verified", worst in fast-growing industries. Here's how the numbers users report compare with healthy ones.

A hard bounce means the address doesn't exist. Mailbox providers read a lot of them as a sign of a spammer: someone who bought a list or guessed addresses. Keep bouncing, and your domain can end up in the spam folder or on a blocklist.

Spam filters look for patterns

Google's 2024 spam update was a turning point. Since then, Gmail and Microsoft have kept getting better at spotting mail that comes from the same sending tools. They look for:

• Generic headers that many senders on one platform share.
• Sending speed that looks like software, not a person.
• IP neighbors. If the address next to yours is flagged, you can be flagged too.
• Similar content across many campaigns from the same platform.

Nobody tells you when this happens. Gmail doesn't send a notice. Your email quietly goes to spam, and users report open rates that were above 40% falling to zero.

How to check if your domain is already hurt

If you've been sending from Apollo, check these four things first.

1. Check your DNS records. Run our free Domain Health Checker to see whether SPF, DKIM and DMARC are in place and correct.
2. Check blocklists. Run our free Blacklist Checker to see whether your domain is on a public blocklist.
3. Look at your bounce rate. Above 5%, you're in the danger zone. Above 10%, you're probably already flagged.
4. Try a domain that never touched Apollo. Send the same email, in a small batch, from a domain that has never sent through it. If the results are very different, the problem is where you send from, not what you wrote.

How to fix it

1. Slow down. Pause big sends while you clean up. Every extra bounce makes things worse.
2. Clean your list. Remove every address that bounced. Don't trust a "verified" label on old data.
3. Fix your records. SPF, DKIM and DMARC should all pass before you send again.
4. Stop sharing your reputation with strangers. Send from infrastructure where the only reputation that counts is yours, so someone else's bad campaign doesn't decide where your email lands.
5. Warm up slowly. A new domain or IP should start small and grow step by step. A big first send from a cold domain looks like spam.

Where Lume fits

The short version

Shared sending used to be good enough. Now, sharing a reputation with strangers is a real risk to your domain.

If your open rates have collapsed, don't rewrite your copy first. Check your list. Check your records. Check where you send from. Then fix what's broken.