Overview
Mailbox providers (MBPs) often have strict rules to protect users from unwanted or undesirable emails. To avoid these spam blockers you need to follow email best practices. If you don't, your emails may bounce and never reach your intended audience, putting your domain health at risk.
Check out the following sections to learn to avoid spam filters and improve email deliverability when you send emails with a mailbox connected to Apollo.
These guidelines represent best practices but don't guarantee the complete elimination of email bounces or spam filtering. Spam filtering is highly individualized. When a recipient marks an email as spam, their email provider may update its filters to block similar messages in the future. As a result, two recipients can receive the exact same email yet experience different filtering outcomes.
Email Deliverability Best Practices
At a high level, there are 2 primary causes for email bounces and mailbox providers marking emails as spam:
Let's dive deeper into how both can impact your deliverability and how you can combat the spam folder.
If you need a quick rundown, jump into Apollo's email deliverability checklist for practical best practices that can help boost your deliverability rates.
Domain Authentication
To prevent malicious senders from spoofing or taking over domains, mailbox providers mandate that all incoming traffic comes from properly authenticated servers and domains. Authentication also helps MBPs track sending reputation by creating common identifiers for all messages from a given source.
Domain authentication won’t guarantee your messages reach the inbox. However, if you don't use domain authentication, you almost guarantee your messages won’t pass spam filters.
To get started:
Authenticate your domain
| Set Up Email Domain Authentication | Set up your SPF, DKIM, and DMARC records to authenticate your domain and ensure high deliverability rates. |
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| Troubleshoot Email Domain Authentication | If you're getting stuck or encounter errors, a few troubleshooting steps can get your domain authentication back on track. |
SPF, DKIM, and DMARC authentication is handled at the domain level, not within Apollo. Apollo doesn't operate its own email servers — all messages are sent directly through your connected email provider. That means domain authentication must be set up through your provider’s DNS settings. Need a refresher on how mailboxes work in Apollo? Start here.
Because domain authentication varies by provider, we recommend using Apollo’s guide to domain authentication to get started. If you run into trouble, reach out to your domain host for help.
For Gmail-specific guidance, check out Google’s tips to avoid getting marked as spam.
Set up a new subdomain
You should never send cold emails from your primary domain. Instead, you can set up a subdomain from which to send your marketing emails.
Each subdomain you create has its own reputation. This means that when you create subdomains for your outreach emails, you add a layer of protection for your root domain.
Don't forget though, that subdomains are still connected to your parent domain. This helps spam scanners identify and trust the domain to be real. However, it means you must continue to follow best practices. If you start spamming contacts from a subdomain, you also put your primary domain at risk.
If you create any new mailboxes from your subdomain, make sure you connect them to Apollo. You can then safely increase the number of emails you send in your campaigns without putting your domain or mailboxes at risk.
One of the most effective ways to keep track of performance and identify how you're doing as a sender is to set up a tracking subdomain. This is a secondary domain name related to your original domain that allows Apollo to redirect a tracking pixel added to emails to track opens. To set up a new tracking subdomain, follow these instructions.
Apollo strongly recommends you set up a tracking subdomain before sending emails and sequences. If you have not set one up, make sure you turn off open and click tracking in Apollo.
Warmup or ramp up your inbox
Use email warmup or inbox ramp up to help build a positive sender reputation and signal to mailbox providers that your emails are safe and trustworthy. Email warmup is best for brand new domains and mailboxes. Inbox ramp up is best for existing mailboxes and domains with prior sending history.
- Inbox ramp up improves email deliverability by increasing outbound email volume over time across the automated or scheduled emails associated with a mailbox. Inbox ramp up aligns your email behavior with mailbox provider standards and reduces the risk of providers identifying your messages as junk or spam.
- Email warmup uses a private network of real inboxes to gradually send, receive, open, and reply to emails on your behalf. This helps build a positive sender reputation and signals to mailbox providers that your emails are safe and trustworthy.
Email Content
Writing effective emails isn’t just about what you say — it's about how you say it. The tips below cover essential strategies to help you craft messages that feel personal, build trust, and avoid triggering spam filters.
| Personalize your messaging | Make sure you research each contact well and always draft your message with the recipient front of mind. Tools like AI research can help you get to know your contacts more deeply. In your messages, talk about what your contacts want to hear and not what you want to tell them. Consider their specific circumstances and goals, and try to meet them where they are at. The more tailored your message is to each specific contact, the more likely they are to engage. |
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| Focus on engagement | To keep clear of spam filters, focus on engagement, not on booking meetings. You get better results sending fewer messages per hour and thoroughly researching each contact — by speaking to their unique goals, responsibilities, and pain points — than you will if you send thousands of contacts the same superficially personalized template:
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| Don't use "bulletproof" templates word-for-word | Avoid copying email templates and subject lines word for word from sales influencers online. However good they might sound, you're not the only one to see and send them. You can take inspiration from Apollo's sample outbound email templates — just make sure you adapt them to your recipient's interests and needs before sending. If you want to stand out from the crowd, put in the extra effort and speak directly to each prospect. |
| Ignore old myths | There's no such thing as a shortlist of words, formatting, and tactics to avoid. The key is to make sure your recipient looks at your message and knows it's not spam. Try to focus on communicating in a professional, personable way. Ask yourself if the email you intend to send is one you would want to receive yourself. Does your message sound authentic? If you were on the receiving end, would you open and reply, or would you click delete? Check out Apollo's master class How to Write Cold Emails Anyone Will Respond To for real truths that move the needle. |
| A/B test your messaging | Always test your messaging to see what works best. You can use A/B tests on Apollo to try multiple versions of a message. For more guidance on A/B testing tactics, watch lesson 5 of the master class Building a World-Class Outbound Program. |
| Include an opt-out link in your email signature | If you don't include an unsubscribe link, you risk violating the US CAN-SPAM Act and may being fined. Customize the text in an opt-out link from your email settings. Apollo then automatically adds the link along with your signature on all of the emails you send in Apollo. Recipients are also more likely to click an unsubscribe link instead of marking your emails as spam. When a recipient unsubscribes, it doesn't affect your overall sending reputation. If they mark you as spam, it does. Check out Configure Your Unsubscribe Email Link to get started. |
FAQs
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Frequently asked questions |
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| Do email sending limits impact email deliverability? | How can I improve email deliverability through content? | Is it better to send from a new domain or my company’s primary domain? |
| How does email warmup and inbox ramp up help deliverability? | Does open or click tracking impact deliverability? | Can I connect multiple mailboxes to Apollo? |
Do email sending limits impact email deliverability?
Yes, email sending limits can directly impact your deliverability. Sending too many emails too quickly — especially from a new or untrusted domain — can trigger spam filters or cause mailbox providers to throttle your messages. Configure sending limits on Apollo to set guardrails. Gradually ramping up your sending volume and staying well within recommended limits helps establish trust and improves inbox placement. Using multiple mailboxes or domains can also help distribute volume safely.
How can I improve email deliverability through content?
Focus on engagement. You get better results sending fewer messages per hour and thoroughly researching each contact than you will if you send thousands of contacts the same superficially personalized template. Remove hard bounces and inactive prospects, and seek to build conversations in cold emails. Avoid spammy formatting, excessive links, and generic templates. Focus on value and relevance — and always include an unsubscribe link. Check out some sample outbound email templates from Apollo to inspire your next message.
Is it better to send from a new domain or my company’s primary domain?
For outbound or cold outreach, always use a subdomain or non-primary domain. This protects your main domain's reputation and allows you to isolate outreach traffic without affecting transactional or support communications.
How does email warmup and inbox ramp up help deliverability?
Email warmup uses a private network of real inboxes to gradually send, receive, open, and reply to emails on your behalf. This helps build a positive sender reputation and signals to mailbox providers that your emails are safe and trustworthy. Warmup is most relevant for brand new domains and mailboxes.
Inbox ramp up gradually increases email volume over time, allowing mailbox providers to build trust in your sending patterns. Starting slow and scaling responsibly is key to avoiding spam flags with a new mailbox. Ramp up is most relevant for existing mailboxes and domains with prior email sending history.
Does open or click tracking impact deliverability?
It can. Some mailbox providers scrutinize tracking links, especially if they're not on a custom subdomain. Always use a custom tracking domain and avoid overusing links in your message. Then, only enable open and click tracking if you have a strong domain reputation and are familiar with email deliverability best practices. Even then, Apollo recommends enabling tracking only on specific, time-bound tests. Once you gain the insights you're looking for, you should deactivate tracking to protect your domain reputation.
Can I connect multiple mailboxes to Apollo?
Yes. Apollo supports linking multiple mailboxes, which helps with deliverability by spreading sending volume across different inboxes. Just make sure each is properly authenticated and warmed up.
Next Steps
| Set Up Email Domain Authentication | Ensure your emails are authenticated by setting up SPF, DKIM, and DMARC records. Proper email domain authentication is critical to prevent your messages from being marked as spam and to protect your domain's reputation. |
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| Use Email Warmup | Use email warmup or inbox ramp up to help build a positive sender reputation and signal to mailbox providers that your emails are safe and trustworthy. Email warmup is best for brand new domains and mailboxes. Inbox ramp up is best for existing mailboxes and domains with prior sending history. |
| Email Sending Limits | Sending limits may be set by your email provider, but you also set Apollo-specific email sending limits. Adhere to recommended email sending limits to maintain high deliverability rates. Apollo suggests sending no more than 50 emails per day per mailbox. |
| Configure an Unsubscribe Link | Include an unsubscribe link in your email signature to comply with regulations like the US CAN-SPAM Act. Apollo allows you to customize this link, making it easy for recipients to opt out so you can protect your sender reputation. |
| Email Deliverability 101 | Join Apollo's live webinar session, Email Deliverability 101, to learn the ABCs of linking your mailbox, setting up domains for maximum deliverability, and monitoring the health of your email performance. |
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