Outbound email limits: 4 caps before the first send

• Before you draft today's onboarding email, write four caps on a note: 60,000 messages a minute, 100 profiles, 5 test addresses, and 50 preview addresses.
• The message rate cap applies to the channel configuration.
• The profile cap applies to subscription state propagation.
• The test address cap applies to immediate test sends.
• The preview address cap applies to daily preview sends.

Four specific limits define the boundaries for your first onboarding email. Customer.io publishes a message rate range of 1 to 60,000 messages each minute for each channel according to Customer.io. Braze states that when a user’s global email subscription state changes, the system propagates that state to other profiles sharing the same email address, up to 100 profiles each change according to Braze. Intercom allows you to send a test message to up to 5 unique email addresses at one time by separating them with commas according to Intercom. Intercom also sets a limit of 50 unique email addresses for a preview email for one message per day according to Intercom. These four values form the core constraints you must record. Each limit is distinct and tied to a specific tool. You do not combine these limits into a single daily total. You track them separately in your pre-send checklist. Understanding which limit applies to which step prevents configuration errors. You set the message rate in the automation settings. You monitor the profile cap when managing shared email addresses. You use the test cap to verify content. You use the preview cap to check rendering. These limits are published by the vendors and are not adjustable by the user beyond the stated ranges. Do not assume a shared daily cap exists across these tools. Do not assume the test send proves final delivery. Do not assume the message rate is a recommendation to send at maximum capacity. Use them to configure your tools correctly. Use them to plan your testing phases. Use them to manage your preview workflows. The limits are the facts. Your job is to apply them.

The first cap to record comes from the Automation concepts & settings documentation. You can set a range of 1 to 60,000 messages each minute for each channel, according to Customer.io. This window defines the maximum throughput your automation can handle on a single channel. When planning your first onboarding email, note that the lower bound is 1 message each minute, while the upper bound is 60,000 messages each minute. This range applies specifically to the channel setting within the automation configuration.

Understanding how recipients enter the automation is just as critical as knowing the speed at which messages send. Subscription preferences do not control whether a person enters your automation or completes other actions like an attribute update, according to Customer.io. Instead, these preferences only affect whether people receive certain messages. This distinction matters for your onboarding sequence because a user might still trigger the start of your automation even if they have unsubscribed from specific email categories. The system processes the entry event and any subsequent attribute updates regardless of the user's current subscription status for particular message types.

For your first onboarding send, focus on the message rate setting first. If you are sending a small batch to a new customer cohort, you are likely operating near the lower end of the 1 to 60,000 messages each minute range. However, if you are launching a broad campaign to a large existing base, you may need to adjust the limit to match your infrastructure capacity. The documentation specifies this as a configurable range for each channel, meaning you can tune it to fit your specific sending volume. Do not assume that a high message rate setting guarantees immediate delivery for every recipient; it simply defines the maximum number of messages the system can dispatch each minute on that channel.

When a user’s global email subscription state changes, Braze propagates that state to other profiles that share the same email address, up to 100 profiles each change, according to Braze. This limit applies specifically to the propagation of subscription state changes within the Email subscriptions documentation. If more than 100 profiles share the same email address, Braze does not guarantee propagation, according to Braze. The 100-profile cap is a hard boundary for this specific state-change mechanism; it does not imply a limit on the total number of profiles in your system, but rather on how many can be updated simultaneously through a single shared address trigger.

For onboarding emails, this rule matters when multiple accounts or team members might be associated with a single shared email address. If your onboarding flow relies on updating subscription preferences across a group of profiles linked to one address, you must account for the 100-profile ceiling. This means you cannot assume that all profiles linked to that address will reflect the new subscription state if the count exceeds the cap.

Additionally, if an address hard bounces because it is invalid or does not exist, Braze marks it invalid and doesn’t attempt further sends, according to Braze.

Intercom’s help documentation for outbound emails defines three distinct boundaries for your pre-launch checks. First, the platform allows you to send a test message to up to 5 unique email addresses at one time, provided you separate the email addresses with commas, according to Intercom. This specific cap on simultaneous test recipients helps you verify rendering and content without cluttering your team’s inboxes. When you move from testing to previewing, the rules shift to a daily volume constraint. There is a limit of 50 unique email addresses that you can send a preview email to for one message per day, according to Intercom. This daily preview cap applies to the specific message you are drafting, ensuring that your internal review group remains manageable while you iterate on copy or design.

Once you are confident in the content and ready to send to your broader audience, the delivery mechanism operates on a multi-queue system. Intercom processes emails in multiple queues, where the first 1,000 go out pretty quickly so you can tell the message is working, then the remainder of the emails are sent out over the course of a few hours, according to Intercom. This initial batch of 1,000 serves as a rapid feedback loop, allowing you to confirm that the message is functioning correctly before the rest of the campaign deploys. Understanding this queue structure is essential for planning your monitoring time. You should be ready to check your analytics or inbox to verify the first 1,000 messages, as the subsequent emails will not arrive in a single burst but will trickle out over several hours.

HubSpot defines the behavior for sequence enrollment in its "Enroll contacts in a sequence" documentation. When manually enrolling a contact, you must choose one of your own connected email accounts as the sender, according to HubSpot. This requirement applies specifically to manual enrollment actions.

The timing of the initial communication follows a specific default rule. By default, the first email in the sequence will send as soon as possible, according to HubSpot. Understanding this default is critical for onboarding workflows where the first touchpoint needs to align with other concurrent customer success activities, such as health score updates or NPS survey timing.

A critical constraint exists regarding daily volume. If a user exceeds their daily send limit, the contact won't enroll in the sequence, according to HubSpot. This rule prevents the sequence from starting if the sender's capacity for that day is exhausted. For a customer success manager preparing to send the first onboarding email, this implies that manual enrollment attempts made after the daily cap is reached will fail to initiate the sequence. The contact will not enter the workflow, meaning no emails will be sent from that sequence.

Consider the interaction between this rule and your broader onboarding strategy. If you are coordinating multiple tools, such as Customer.io for automated drips and HubSpot for manual follow-ups, ensure that your HubSpot manual enrollments do not conflict with your daily sending capacity. The "as soon as possible" default for the first email means that any delay in enrollment due to hitting the daily limit directly delays the customer's first touchpoint. This delay can impact the perceived speed of onboarding.

Imagine one onboarding message. You set the channel rate at the low end of the published range, then check a shared address that touches 100 profiles. You send the test to 5 addresses. You send the preview to 50 addresses. After launch, you watch the first 1,000 messages leave quickly and the rest follow over a few hours. None of these figures is a combined daily total. Each one belongs to its own tool and its own step.

The four caps are Customer.io's message-rate range for each channel, Braze's 100-profile cap, Intercom's 5-address test limit, and Intercom's 50-address preview limit. These figures come from the tools you will use to send and test the message. Keep the note visible while you configure the first send, and match the draft to your onboarding project plans.

What message range does Customer.io state each minute?

Customer.io documents that you can set a range of 1 to 60,000 messages each minute for each channel according to Customer.io. This setting applies specifically to the automation concepts and settings outlined in their documentation. Keep this range in mind when configuring your outbound email throughput.

How many profiles does Braze mention for one email-address change?

Braze mentions up to 100 profiles each change when it propagates a global email subscription state to other profiles that share the same email address, according to Braze.

How many test addresses does Intercom allow at one time?

Intercom allows up to 5 unique email addresses for a test message at one time if you separate them with commas, according to Intercom.

How many preview addresses does Intercom allow for one message per day?

Intercom sets a limit of 50 unique email addresses that you can send a preview email to for one message per day according to Intercom. This daily cap applies to preview emails for a specific message. Track your preview sends to stay within this documented threshold.

What does HubSpot say happens when a user exceeds the daily send limit?

HubSpot explains that if a user exceeds their daily send limit, the contact won't enroll in the sequence according to HubSpot. This behavior is specific to the enrollment process described in their sequence documentation. Monitor your daily send volume to prevent unintended enrollment failures.

This post is general operational information, not legal advice about notice periods or renewal clauses. It does not promise that any method keeps a customer. A review model checked the facts once, and that check can miss errors, so open the sources before you act.