IP addresses: shared vs dedicated

You can use our shared IP pools or dedicated IPs to send messages to your customers.

Shared IP pool (default)

By default, we add email domains to Customer.io’s shared IP address pool to send emails. We manage and monitor multiple IP pools and remove domains that perform poorly to maintain high deliverability.

Third-party blocklist results for shared IPs

Tools like mail-tester and multi-blocklist checkers sometimes show a shared Customer.io IP on a third-party blocklist. Results from these tools often don’t match real-world delivery, so a listing in one of them doesn’t necessarily explain why a message reached the spam folder. Customer.io monitors the shared and dedicated IPs we control for blocklist activity and works to mitigate listings.

Listings on your own sending domain are different. A Spamhaus domain listing blocks delivery to most major email providers, and you need to resolve it yourself.

Google Postmaster Tools shows how Gmail treats your email once you send Gmail enough volume for its charts to fill in. You may want to set it up before you need it. For new senders, inbox placement depends on factors like your domain reputation and whether you send transactional email from its own domain.

If you see real bounces or other delivery problems, contact our support team at win@customer.io and include an example message.

Send from transactional IP pool

We also maintain a separate, transactional IP address pool. This pool has higher standards—stricter bounce and spam thresholds—than our default, shared IP pool. This ensures that your transactional messages achieve the highest deliverability. Only domains used with the transactional service can send emails over this IP pool.

To use our transactional IP pool, you’ll need a separate sending domain dedicated to transactional messages. Before you ask us to add your domain to the transactional IP pool, make sure that:

• Your domain is fully verified.
• Your domain is fully separated from your marketing activities. It isn’t used in automations or broadcast messages.
• You’ve built at least one transactional message, and it’s set to send from your transactional domain.

When your domain meets these requirements, request to add it to the transactional IP pool:

1. Go to Settings > Workspace Settings > Email and select your transactional domain.
2. In the Mail servers section, select Shared IP pool - transactional.
3. Describe the type of emails you’ll send from the domain, and type the domain name to confirm.
4. Click Request Shared IP pool - transactional.

Customer.io reviews your request and moves your domain to the transactional pool when we approve it. You can’t request the transactional IP pool during a trial.

Send from dedicated IPs

Sending from a dedicated IP is the only way to take full control over your sending reputation. While we go to great lengths to ensure the health of our shared IP network, there is always the chance that your deliverability could be impacted by the sending habits of other Customer.io accounts.

Benefits of a dedicated IP

One of the main benefits of using a dedicated IP address is that it allows organizations to manage their own IP reputation. This means that they can control how their emails are perceived by email providers and recipients. By sending emails from a dedicated IP address, you can build a positive reputation directly with email providers at the IP level.

A dedicated IP address can also improve email deliverability. This is because the IP address is exclusively used for your email sending, and there is no risk of it being blocklisted due to other senders’ actions. This can increase the likelihood of emails being delivered to recipients’ inboxes, rather than being filtered into the spam folder.

Requirements for sending from a dedicated IP

To send from a dedicated IP, your workspace needs to send at least 5,000 emails per day or 50,000 emails per week.

Customer.io assigns dedicated IPs based on your current sending volume, not the volume you expect to send. We set this threshold because low email volume can result in unpredictable deliverability performance with inbox providers.

Cost of a dedicated IP

Premium level customers can request up to three dedicated IPs at no extra cost. Outside of that, each dedicated IP is $50 per month.

Request a dedicated IP

If you haven’t met the volume requirement, contact your Customer Success Manager (CSM) or success@customer.io about when a dedicated IP makes sense.

If you’ve met the volume requirement within the past week, you can request a dedicated IP from your email settings:

1. Go to Settings > Workspace Settings > Email and select the domain you want to send from.
2. In the Mail servers section, select Dedicated IPs.
3. Enter your current daily send volume, add any comments, and click Request Dedicated IPs.

Customer.io reviews your request, sending volume, and any other influencing factors before beginning the warming process. While we review your request, the domain shows Your request is being reviewed. To change your request, click Request a change.

Set up and IP Warming

At Customer.io, we completely handle the setup, warming, and configuration of your dedicated IPs. All that is required from you is to send email normally, and we’ll take care of the rest. Depending on your volume, the warming process can take 30-45+ days. Senders with a higher volume generally move through the warming stages more quickly.

During warming, you will send from your currently assigned, shared IPs as well as your new dedicated IPs. As time progresses, we will slowly increase the amount of email sent via your dedicated IP until warming is complete. When your IP is ready, we’ll shift all sending to your dedicated IP and let you know you’re good to go.