Quick answer: A paid Google Workspace mailbox can send 2,000 messages a day (500 on a trial); personal Gmail about 500. An Exchange Online mailbox can send to 10,000 recipients a day, but all mailboxes in a Microsoft 365 tenant share one external cap of 500 × licences0.7 + 9,500: 10,000 for one licence. These are rolling 24-hour ceilings, not targets.
Every limit below was read on Google’s and Microsoft’s own pages on 28 September 2026: Google Workspace, personal Gmail, the Gmail API and SMTP relay; Exchange Online, the Microsoft 365 tenant external recipient rate limit (TERRL) and Outlook.com. Then a worked calculation turns them into a mailbox count.
How many emails can my AI email agent send per day from Gmail or Outlook?
An AI email agent sends one-to-one messages: one recipient per message, each prospect at most once a day. For that pattern the smallest applicable daily count binds first.
| Account type | Daily ceiling that binds a one-to-one agent | Other daily limits on the same account | Window and rate |
|---|---|---|---|
| Google Workspace, paid | 2,000 messages per user | 10,000 total recipients; 3,000 external recipients; 3,000 unique recipients, of which 2,000 external; 1,500 for mail merge | Rolling 24 hours. Gmail API: 6,000 quota units per minute per user per project (Cloud projects created from 1 May 2026), messages.send = 100 units (60 sends a minute) |
| Google Workspace, free trial | 500 messages per user | 500 unique external recipients | Rolling 24 hours |
| Google Workspace SMTP relay | 10,000 messages per user | 10,000 unique recipients per user; 100 recipients per SMTP transaction; organisation-wide 4.6 million non-unique recipients | 24 hours; organisation-wide 319,444 per 10 minutes. Counted separately from Gmail user limits |
| Personal Gmail | 500 emails a day | More than 500 recipients in one email also triggers the limit | Sending resumes “within 1 to 24 hours” |
| Exchange Online mailbox (Microsoft 365 Business Basic, Standard and Premium; Microsoft 365 E3/E5; Office 365 E1, E3/E5 and F3; Exchange Online Plan 1, Plan 2 and Kiosk) | 10,000 recipients per day | Recipients per message customisable up to 1,000 | Past 24 hours; 30 messages per minute |
| Exchange Online tenant, external recipients (TERRL) | 500 × (non-trial email licences0.7) + 9,500, shared by every mailbox | 10,000 for 1 licence; 12,006 for 10; 72,446 for 1,000 | 24-hour sliding window |
| Exchange Online trial tenant | 500 external recipients (Exchange Team post) or 5,000 (Learn page) | The two Microsoft pages disagree; see below | 24-hour sliding window |
| Microsoft 365 default onmicrosoft.com domain | 100 external recipients per organisation | Applies only to mail sent from the onmicrosoft.com address | 24-hour rolling window |
| Outlook.com with a Microsoft 365 subscription | 1,000 non-relationship recipients (people never emailed before) | 5,000 daily recipients; 500 recipients per message; lower for non-subscribers | Daily |
The row most people skip is the TERRL row: on Exchange Online, the per-mailbox 10,000 is not the ceiling for outbound prospecting, because every mailbox in the tenant draws external recipients from one shared pool. On Google Workspace, the Gmail sending-limits page states its limits per user and lists no tenant-wide external cap of that kind; the organisation-wide figures Google does publish belong to the SMTP relay service.
Messages, recipients or unique recipients: what each limit counts
Google counts three ways. Google’s page defines total recipients as each address counted every time a message is sent: “5 messages sent to 10 addresses count as 50 total recipients”. Unique recipients count each address once per day, so the same 5 messages to 10 addresses count as 10 unique recipients. The external recipients row covers “email addresses outside your primary domain, including domain aliases and alternate domains”. Alias sends, delegated sends and vacation-responder messages all count toward a user’s limits; auto-forwarded messages do not.
Microsoft’s per-mailbox limit counts recipients, per user. The recipient rate limit is “the maximum number of recipients that a user or mailbox can send to in a 24-hour period”, applied “to all outbound and internal messages”. A distribution group stored in the organisation’s address book counts as one recipient; a group stored in a mailbox’s Contacts folder counts each member. Mail sent from another mailbox through permissions “is counted for the delegate with rights and not the mailbox that is being sent from”, which matters if an agent sends on behalf of a rep’s mailbox using delegated access.
Microsoft’s tenant limit counts every external recipient, not unique ones. The Exchange Team’s FAQ answers directly: 1,000 messages to the same external address in a day count as 1,000, because TERRL “doesn’t track unique external recipients”, and group members are counted after the group and its nested groups are expanded. Among the exclusions Microsoft lists: journaling messages, automatic replies, delivery status notifications, mail sent through Azure Communication Services email or High-volume Email, and Microsoft cloud-app notifications.
The windows roll rather than reset at midnight. Google says its daily limits “are applied over a rolling 24-hour period, not a set time of day”. Microsoft’s example: a user who sends to 5,000 recipients at 9:00 am, 2,500 at 10:00 am and 2,500 at 11:00 am reaches 10,000 and “won’t be able to send messages again until 09:00 AM the next day”.
For the one-to-one pattern an agent uses, the counts collapse: one recipient per message and no prospect emailed twice in a day means messages, total recipients and unique recipients are the same number. On paid Workspace that makes 2,000 the binding figure, since the 2,000-message cap and the 2,000 unique-external cap arrive together.
Microsoft’s tenant external recipient rate limit, as at 28 September 2026
The Exchange Online tenant external recipient rate limit (TERRL) is “the maximum number of external recipients a tenant can send to per day (24-hour sliding window)”, in the words of Microsoft’s Exchange Online limits page. External means any domain not accepted by the tenant, including other Microsoft 365 tenants. The Exchange Team post frames the quota as the limit for “a tenant in good standing” and says further restrictions can apply because of factors such as suspicious sending behaviour, sending spam, or fraudulent or excessively late payments, so the formula is a maximum, not a guarantee.
The standard quota comes from a formula in Microsoft’s Introducing Exchange Online Tenant Outbound Email Limits post: 500 × (number of non-trial email licences0.7) + 9,500. Any licence for, or including, Exchange Online or Exchange Online Protection counts, whether or not it is assigned to a user. Microsoft publishes these sample values:
| Non-trial, non-EDU email licences | Tenant external recipients per 24 hours | External recipients per licence |
|---|---|---|
| 1 | 10,000 | 10,000 |
| 2 | 10,312 | 5,156 |
| 10 | 12,006 | 1,201 |
| 25 | 14,259 | 570 |
| 100 | 22,059 | 221 |
| 1,000 | 72,446 | 72 |
| 10,000 | 324,979 | 32 |
| 100,000 | 1,590,639 | 16 |
The third column is our division of Microsoft’s figures, rounded. It shows the design: a second Exchange Online licence adds 312 external recipients a day to the tenant, not another 10,000. Microsoft’s post says the same in words: more licences raise the tenant’s daily external limit, but at a decreasing rate per licence.
Rollout status as at 28 September 2026. The post states that TERRL “is fully implemented for tenants in WW environment” and that it has been postponed for the GCC, GCCH, DoD and 21Vianet environments, with dates to follow. An update dated 13 August 2026 says Microsoft is changing how the quota is calculated “for certain tenants”, with those changes beginning to roll out from 14 September 2026. The post then lists:
- Trial tenants: 500 total external recipients a day, regardless of licence count.
- Newly created tenants: 10% of the standard quota for a tenant less than 31 days old, 25% at 31 to 60 days, 100% after 60 days.
- Tenants with free Education licences: 500 × (purchased email licences0.7 + free EDU licences0.3) + 9,500.
- All other tenants: the standard formula above.
The trial figure conflicts between Microsoft’s own pages. The Exchange Online limits page on Microsoft Learn still says “the limit for trial tenant is capped at 5,000 external recipients per day”. The Exchange Team post says 500. We read both on 28 September 2026 and could not find a Microsoft statement reconciling them, so plan for the lower figure. Your tenant’s actual quota, usage and whether enforcement is enabled appear in the Exchange admin centre under Reports, Mail flow, Tenant Outbound External Recipients. When the cap is exceeded, senders receive 550 5.7.232 (trial tenants) or 550 5.7.233 (non-trial tenants).
The per-mailbox external limit is cancelled. Microsoft had separately announced a Mailbox External Recipient Rate Limit. On 6 January 2026 the Exchange Team published that it is cancelled indefinitely. The 10,000-recipient per-mailbox limit and TERRL are what apply.
When the answer changes: trials, new tenants, consumer accounts
The headline numbers assume a paid, established account on your own domain. Five conditions move them.
- A Google Workspace trial. A trial runs for 14 days and is limited to 10 users, per Google’s About your Google Workspace free trial page. Trial users are held to 500 messages and 500 unique external recipients a day, and Google says limits “aren’t increased during the free trial period”. After converting, limits rise automatically once the domain has cumulatively paid at least USD 100 (plus the domain cost, if the domain was bought from Google), and “it can take up to 75 days after meeting this payment threshold” for the increase to arrive.
- A new Microsoft 365 tenant. Under the changes Microsoft said would begin rolling out from 14 September 2026, a tenant younger than 31 days receives 10% of its calculated external quota, so a one-licence tenant gets 1,000 external recipients a day; 31 to 60 days gives 25%, or 2,500. Whether the change has reached a given tenant shows in its Exchange admin centre report.
- The onmicrosoft.com address. Mail sent from a tenant’s default onmicrosoft.com domain is limited to 100 external recipients per organisation in a rolling 24 hours, with NDR code 550 5.7.236. Microsoft says these domains “should only be used for testing purposes”. An agent must send from a custom domain.
- A consumer mailbox. Personal Gmail stops at 500 emails a day. Outlook.com gives Microsoft 365 subscribers 5,000 daily recipients but only 1,000 non-relationship recipients, and every first-touch prospecting email goes to a non-relationship recipient. Microsoft says limits may vary based on usage history and are lower for non-subscribers, and does not publish the non-subscriber figures.
- A breach of the limit. Google says a user who hits a limit “can’t send new messages for up to 24 hours” and that accounts sending spam “might be permanently restricted from sending email”. Over the TERRL, the whole tenant’s external mail bounces until the 24-hour volume falls below quota.
How many mailboxes does an AI agent sending 1,500 contacts a day need?
Substitute your own inputs at each step; the arithmetic is the method.
Step 1: daily messages from the sequence. Assume the agent enrols 1,500 new contacts a day into a three-step sequence, with steps on different days, so no contact receives two messages on one day. Once the sequence has been running longer than its final step’s delay, each day carries step 1 for today’s contacts, step 2 for an earlier cohort and step 3 for an earlier one still: 1,500 × 3 = 4,500 messages a day. It is an upper bound: contacts who reply or bounce leave early.
Step 2: add reply handling. Prospects who answer receive further messages from the agent, and those count too. Our example input is 4% of the day’s 1,500 contacts replying and each reply drawing 2 agent messages: 1,500 × 0.04 × 2 = 120. The 4% is an input to show the arithmetic, not a benchmark; use your own reply log. Daily demand D = 4,500 + 120 = 4,620 messages, each to one external recipient.
Step 3: set the headroom per mailbox, and why. The safety margin on this page is not a flat percentage, because neither Google nor Microsoft publishes a recommended utilisation, and a figure like “stay at 80%” would be one we made up. Instead, the headroom H is the traffic that counts against the mailbox but that the agent does not schedule. Google names it: alias sends, delegated sends and vacation-responder messages all count toward a user’s limit. Microsoft counts delegated sends against the delegate. If the agent sends from a rep’s own mailbox, the rep’s manual email counts as well. Measure H as the mailbox’s non-agent sends on its busiest day in the last 30 days (Google points admins to the Apps usage user report for per-user sent counts; Microsoft’s post points to message trace in the Exchange admin centre to find top senders). The reason to reserve it rather than absorb it: when a Workspace mailbox reaches a limit, it cannot send anything for up to 24 hours, including replies to prospects who just answered. Our example input is H = 150, and for the Microsoft tenant check we treat all 150 as external, which is the cautious case.
Step 4: divide by the planning ceiling and round up.
- Google Workspace, paid: 4,620 ÷ (2,000 − 150) = 4,620 ÷ 1,850 = 2.497, so 3 mailboxes.
- Google Workspace, trial: 4,620 ÷ (500 − 150) = 4,620 ÷ 350 = 13.2, so 14 mailboxes. Without headroom it would be 4,620 ÷ 500 = 9.24, so 10; the margin matters most where the ceiling is lowest. Either count runs into another trial rule: Google limits a Workspace trial to 10 users, and adding an 11th user ends the trial and starts billing, so at this volume a trial cannot carry the load, and the paid limits then arrive only after the USD 100 threshold and up to 75 days.
- Exchange Online, established tenant: 4,620 ÷ (10,000 − 150) = 0.469, so 1 mailbox. Tenant check: 4,620 + 150 = 4,770 external recipients against a one-licence TERRL of 10,000, which fits. Rate check: 4,620 messages at 30 a minute is 154 minutes of sending at the maximum rate.
- Exchange Online, tenant under 31 days old: the one-licence quota falls to 1,000, below the 4,770 needed. Solving 10% × (500 × L0.7 + 9,500) ≥ 4,770 gives L = 490 licences. At 31 to 60 days, 25% of the quota needs L = 68. The practical answer for a new tenant is to wait, or ramp volume with the quota, not to buy licences.
The same method at three volumes, with reply handling scaled at the same example rate and H = 150 per sending mailbox:
| New contacts a day | Daily demand D (3 steps + replies) | Workspace paid mailboxes | Workspace trial mailboxes | Exchange, tenant over 60 days old | Exchange licences needed, tenant under 31 days | Exchange licences needed, tenant 31 to 60 days |
|---|---|---|---|---|---|---|
| 500 | 1,500 + 40 = 1,540 | 1 (1,540 ÷ 1,850 = 0.83) | 5 (1,540 ÷ 350 = 4.4) | 1 mailbox, 1 licence (1,690 of 10,000 external) | 47 | 1 |
| 1,500 | 4,500 + 120 = 4,620 | 3 (4,620 ÷ 1,850 = 2.50) | 14 (4,620 ÷ 350 = 13.2); above the 10-user trial cap, so not available | 1 mailbox, 1 licence (4,770 of 10,000 external) | 490 | 68 |
| 5,000 | 15,000 + 400 = 15,400 | 9 (15,400 ÷ 1,850 = 8.32) | 44 (15,400 ÷ 350 = 44.0); above the 10-user trial cap, so not available | 2 mailboxes, 37 licences (15,700 external against a quota of 15,762) | 3,376 | 789 |
The bottom row shows the Microsoft pattern at scale: two Exchange mailboxes have ample per-mailbox capacity for 15,400 messages, but the tenant needs 37 licences before its shared external pool reaches 15,700. On Google Workspace the cost grows with mailboxes; on Exchange Online it grows with licences, much faster than linearly. What those seats cost against an AI SDR’s own pricing is covered in how AI SDR pricing treats mailboxes, seats and messages.
A sending limit is a ceiling, not a deliverability target
Every number above is the most mail the provider’s servers will accept from you. None of it says how much the receiving inboxes will accept, and the receiving side has its own rules. Google’s email sender guidelines ask every sender to keep spam rates in Postmaster Tools below 0.3%, and add requirements for senders of more than 5,000 messages a day to personal Gmail accounts. Google’s sender FAQ says those 5,000 are counted across the same primary domain. So if close to 5,000 or more of the 15,400 daily messages in the bottom row went to personal Gmail addresses, the domain would be a bulk sender whether the mail left from 9 mailboxes or 90. Splitting volume across mailboxes changes which platform limit you meet; it does not change who you are to Gmail.
The recipient-side rules (SPF, DKIM, DMARC, one-click unsubscribe and spam-rate thresholds at Gmail, Outlook and Yahoo) are set out in our guide to the Gmail and Outlook bulk-sender rules for 2026, and this page does not repeat them. Microsoft is blunter than Google: its limits page says customers sending “legitimate bulk commercial email” should use specialist third-party providers.
The practical reading: a mailbox count that only just clears the platform limit is a plan to run each inbox at the edge of what its provider tolerates. Whether adding more domains and inboxes is a good response to falling engagement is a strategy question, taken up in why reply rates fall as AI outbound volume rises.
What an AI email agent should do with these numbers
If you are configuring the agent yourself, the method above is complete. Three controls turn it into behaviour:
- Keep a rolling 24-hour counter per mailbox in the provider’s own units (messages and unique external recipients on Workspace, recipients on Exchange), plus one tenant-wide external counter for Microsoft 365 that every mailbox writes to.
- Stop scheduling at the planning ceiling (limit minus H), not at the limit, so a prospect who answers never meets a suspended mailbox.
- Spread sends through the day. A 9:00 am burst is still counted at 8:59 am the next day. Exchange Online also caps submission at 30 messages a minute: Microsoft’s page says excess is throttled and carried over to the following minutes, and SMTP client submissions above the rate are rejected for retry.
The running cost is the part people underestimate: counters, per-account ceilings, trial and new-tenant conditions, and a quarterly check that neither provider has moved a limit, since both say they can. At higher volumes the question stops being “how many mailboxes” and becomes which channel should carry the next touch. Zian works across more than 10,000 leads a day. Its agents run on phone, SMS, email and WhatsApp, and SmartReach AI™ orchestrates channel, timing and follow-up pacing, so email is one channel in the sequence rather than the only one. The trade-off between an email-only tool and a multichannel agent is laid out in AI email outreach tools compared with AI sales agents.
Frequently asked questions
How many emails can I send per day from Google Workspace?
A paid Google Workspace user can send 2,000 messages a day, counted over a rolling 24 hours, with separate caps of 10,000 total recipients, 3,000 external recipients and 3,000 unique recipients (2,000 of them external). A trial account is limited to 500 messages. The figures are on Google’s Gmail sending limits in Google Workspace page.
What is the Exchange Online tenant external recipient rate limit?
It is a tenant-wide cap on external recipients over a 24-hour sliding window. Microsoft’s Exchange Team post gives the standard quota as 500 × (non-trial email licences to the power 0.7) + 9,500, which is 10,000 for one licence and 72,446 for 1,000 licences.
Is the Microsoft trial tenant limit 500 or 5,000 external recipients a day?
Microsoft’s two pages disagree as at 28 September 2026. The Exchange Online limits page says trial tenants are capped at 5,000 external recipients a day; the Exchange Team post, updated 13 August 2026, says trial tenants are limited to 500 regardless of licence count, with changes rolling out from 14 September 2026. Plan for 500 and read your tenant’s own report in the Exchange admin centre.
Does sending through the Gmail API get around Workspace sending limits?
Google’s Workspace sending-limits table includes a row for recipients per message sent with the Gmail API (500), so the API is listed inside those limits rather than beside them. The Gmail API quota page adds a rate limit on top: 6,000 quota units per minute per user per project for Google Cloud projects created on or after 1 May 2026 (projects that used the API between November 2025 and April 2026 keep their previously set quotas), with messages.send costing 100 units, which works out to 60 sends a minute per user.
What happens when an AI agent hits the Gmail sending limit?
Google says the user sees an error such as You have reached a limit for sending email and cannot send new messages for up to 24 hours, although incoming mail and other Google services keep working. An agent answering prospects from that mailbox stalls too.
How many emails can I send per day from Outlook.com?
Microsoft’s Outlook.com sending limits page gives Microsoft 365 subscribers 5,000 daily recipients, 500 recipients per message and 1,000 daily non-relationship recipients, meaning people you have never emailed before. Limits are lower for non-subscribers.
Should I aim to send right up to the limit?
No. The platform limits are ceilings on what the service will accept, not a volume that inboxes will welcome. Recipient-side rules are separate: Google’s email sender guidelines apply extra requirements to anyone sending more than 5,000 messages a day to personal Gmail accounts, counted across the whole primary domain, and ask all senders to keep spam rates below 0.3%.
Where every figure on this page comes from
| Figure | Who published it | Link | Date read |
|---|---|---|---|
| Workspace 2,000 messages per user a day; 500 trial; 1,500 mail merge; 10,000 total, 3,000 external, 3,000 unique (2,000 external; 500 external trial) recipients; 10,000 auto-forwarded; 500 recipients per Gmail API message; rolling 24 hours; up to 24-hour suspension; USD 100 and 75-day paid-limit increase | Gmail sending limits in Google Workspace | 28 September 2026 | |
| Workspace free trial: 14 days, up to 10 users; an 11th user ends the trial | About your Google Workspace free trial | 28 September 2026 | |
| SMTP relay 10,000 messages and 10,000 unique recipients per user; 100 per transaction; 4.6 million and 319,444 organisation-wide | SMTP relay service | 28 September 2026 | |
| Gmail API 6,000 quota units per minute per user per project (projects created on or after 1 May 2026); messages.send 100 units | Gmail API usage limits | 28 September 2026 | |
| Personal Gmail 500 emails a day; 500 recipients per email; 1 to 24 hours | Limits for sending and getting mail | 28 September 2026 | |
| 0.3% spam rate; more than 5,000 messages a day to Gmail accounts | Email sender guidelines | 28 September 2026 | |
| 5,000 counted across the same primary domain | Email sender guidelines FAQ | 28 September 2026 | |
| Exchange Online 10,000 recipients per day; 30 messages per minute; up to 1,000 recipients per message; trial tenant 5,000 external; 9:00 am rolling-window example | Microsoft | Exchange Online limits | 28 September 2026 |
| TERRL formula and sample values (10,000 to 1,590,639); trial 500; 10% and 25% new-tenant quotas; 14 September 2026 rollout; NDR 5.7.232 and 5.7.233 | Microsoft Exchange Team | Introducing Exchange Online Tenant Outbound Email Limits | 28 September 2026 |
| Mailbox External Recipient Rate Limit cancelled, 6 January 2026 | Microsoft Exchange Team | Exchange Team post on the mailbox external limit, 6 January 2026 | 28 September 2026 |
| onmicrosoft.com 100 external recipients per 24 hours; NDR 5.7.236 | Microsoft Exchange Team | Limiting Onmicrosoft Domain Usage for Sending Emails | 28 September 2026 |
| Outlook.com 5,000 daily recipients; 500 per message; 1,000 non-relationship recipients | Microsoft | Sending limits in Outlook.com | 28 September 2026 |
| Per-licence column; mailbox and licence counts in the worked calculation | Zian, calculated from the Google and Microsoft figures above; reply rate (4%) and headroom (150) are stated example inputs | This page, Steps 1 to 4 | 28 September 2026 |
| More than 10,000 leads a day | Zian (first-party) | First-party figure released by Zian; no external page | 28 September 2026 |
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