How to Send Mass Email in Outlook: 3 Ways and Their Limits

To send a mass email in Outlook, put the addresses in Bcc (blind carbon copy), add a contact list to Bcc, or use Word's mail merge.

Each method sends from your own mailbox, so Microsoft's limits apply: 500 recipients in one email by default, and 5,000 or 10,000 a day, depending on the account.

A garden centre near Shrewsbury has 1,400 loyalty-card customers to tell about its spring plant fair. It needs one mass email that reaches all of them while every address stays private.

Three mass email methods compared

How to send mass email in Outlook without others seeing

Put every customer address in Bcc, and nobody on the email can see who else received it. For the garden centre's list:

1. Open a new email. If Outlook hides the Bcc field, switch it on first.
2. Put your own address in To, so the email has a visible recipient.
3. Paste up to 499 addresses into Bcc: the To address counts towards the 500. So 1,400 addresses need three emails: 499, 499 and 402.
4. Check that no customer address sits in To or Cc, then click Send.

The weak point is one slip. Pasting the list into either field by mistake shows every address to everyone. In the UK, that can be a personal data breach, and the ICO (Information Commission's Office) has fined organisations for it.

The fines, and the Bcc steps for each Outlook version, are in CC and BCC meaning in email.

How to create a contact group or distribution list in Outlook

A contact group stores a set of addresses under one name, so you type the name instead of 1,400 addresses. Many people say distribution list. Classic Outlook calls it a contact group; Outlook.com and new Outlook use contact list.

In new Outlook, Outlook on the web and Outlook.com:

1. Select People in the side panel.
2. Select the arrow next to New contact, then New contact list.
3. Type a name, add people under Add recipients and select Create.

In classic Outlook, go to People and select New Contact Group on the ribbon. Name the group, add people with Add Members and select Save & Close (Microsoft Support).

To send, type the list's name in Bcc, not in To. With a contact group in To, every member sees every other member's address, as a Microsoft community moderator points out.

A contact list still counts every member

The list saves typing, not recipients. On Microsoft 365, each member of a personal contact list counts as a separate recipient. So a 1,400-name list breaks the 500 limit as surely as pasted addresses would (Microsoft Learn). It would need three lists, none over 499.

A distribution list that your Microsoft 365 admin creates in the organisation's shared address book works differently. It counts as one recipient in a single email. Its members still count one by one towards your organisation's daily limit for external recipients.

Mail merge: a separate email for each person

Mail merge sends each person their own email, addressed only to them, so it needs no Bcc at all. Word fills a template from a spreadsheet, so «First name» turns into each customer's own first name, and passes one email per row to Outlook.

Word's merge works only with classic Outlook for Windows, as how to do a mail merge in Outlook shows step by step. New Outlook has a simpler option: while writing an email, choose Start mail merge from the arrow beside Send. It sends everyone a separate copy but cannot add names (Microsoft Support).

A merge is slower than Bcc, because every copy is a separate message. Microsoft 365 sends 30 messages a minute from one mailbox and holds the rest for the following minutes. Sent this way, 1,400 copies would take about 47 minutes to leave (Microsoft Learn).

The template, the spreadsheet and the point where a merge stops being enough are covered in how mail merge works.

Outlook sending limits: how many people can you email?

Outlook lets you address 500 people per email. The daily cap is 5,000 on Outlook.com with a Microsoft 365 subscription and 10,000 for a Microsoft 365 business account.

Account	Recipients in one email	Recipients a day	Other limits
Outlook.com with a Microsoft 365 subscription	500	5,000	No more than 1,000 people you have never emailed before
Outlook.com without a subscription	Lower, not published	Lower, not published	None published
Microsoft 365 business account	500 by default; an admin can set 1 to 1,000	10,000 in any 24 hours	30 messages a minute

Sources, as of 25 October 2026: Sending limits in Outlook.com, Microsoft's Exchange Online limits (last updated 19 October 2026). The 500 default comes from Microsoft's guide to outbound sending limits.

Any new Outlook.com account, with or without a subscription, starts on a low sending quota that rises once the account builds a history.

Every address counts against the daily figure. A Bcc email to 500 people uses 500 of the day's allowance, and so does a merge to 500.

Can you send 1,000 emails from Outlook? With a business account, yes: Bcc batches of 499, or a merge of 1,000 copies, stay well inside that 10,000.

On Outlook.com with a subscription, 1,000 is also the daily cap for first-time recipients. A first send to 1,000 new addresses uses all of it.

When a business mailbox reaches 10,000, further emails bounce back with an error. Sending resumes once the total for the past 24 hours drops below the limit.

Why mass email from Outlook puts your mailbox at risk

If Microsoft decides a mailbox is sending too much or sending spam, it can block that mailbox from sending any email.

Its outbound spam guidance calls bulk email through Microsoft 365 an unsupported use, allowed on a "best-effort" basis only. It also advises against sending to a large list of Bcc recipients (Microsoft Learn, updated 21 May 2026).

Staying under the limits is no guarantee

Some of the limits that block accounts are not published. Microsoft keeps them private so that spammers cannot work around them, and it raises or lowers them as it sees fit.

On Microsoft 365, the blocked user appears on the Restricted entities page until an admin releases them, or, under some policies, until the next day (Microsoft Learn).

Email that Microsoft judges to be spam leaves through a separate high-risk delivery pool. Many receiving services refuse mail from that pool, so it may never arrive (Microsoft Learn).

Your main domain takes the complaints

Microsoft advises against bulk email from your primary domain, because it can affect delivery of the domain's regular email (Microsoft Learn). It suggests a subdomain used only for bulk email, such as m.contoso.com. Set it up with SPF, DKIM and DMARC: the three records that let receiving services check an email really comes from your domain.

Each spam complaint about the plant fair email would count against the centre's main domain. How mailbox providers score a domain is explained in email sender reputation.

To stay out of spam folders, send from an authenticated domain, only to people who asked for your email, with a working unsubscribe link. The other signals filters read are in why emails go to spam.

Marketing email needs a way out

Under PECR (Privacy and Electronic Communications Regulations), every marketing email must include a valid address where people can opt out (ICO). From Outlook, that means a line asking people to reply. Each reply then has to come off the list by hand before you send again.

When to move from Outlook to an email platform

Move when the email turns into marketing, goes out regularly or reaches more people than one Outlook email holds. Outlook still suits a short notice with the same words for everyone.

The garden centre's two jobs show the line. Telling 40 landscapers that trade deliveries move to Thursdays fits one Bcc email.

The plant fair announcement is different: it is the first of a monthly offers email to 1,400 customers. It is marketing, it needs three Bcc batches every month, and Outlook cannot show who opened it or clicked.

From Outlook contacts to MailGraf

Your contacts move across as a CSV (comma-separated values) file. In MailGraf, the move takes three steps:

1. Export your contacts from Outlook. Classic Outlook does it under File > Open & Export > Import/Export: choose Export to a file, then Comma Separated Values. New Outlook has Export contacts under People, and Outlook.com puts it under Manage contacts (Microsoft Support).
2. Delete anyone you have no permission to email for marketing.
3. In MailGraf, import the file under Imports > New import; the file import help article walks through Mapping and Permission.

On 25 October 2026 we passed the header row of Microsoft's sample Outlook contacts file (92 columns) through the matching code behind MailGraf's Mapping step. The test used the view of a new account with no custom fields. First Name, Last Name and E-mail Address matched to First name, Last name and Email. The other 89 stayed on Skip, so an export goes in without deleting columns.

The reply-and-delete routine ends there: every copy carries its own unsubscribe link, and a customer who uses it drops out of next month's audience.

Microsoft's subdomain advice is the setup MailGraf uses: connect a subdomain such as offers.yourgardencentre.co.uk with four nameserver records, and MailGraf manages the three records (add a sending domain).

Outlook's 499-address batches have no counterpart either: the monthly plan has no daily sending limit, only the monthly allowance, and contacts are unlimited. Before the next plant fair, compare the loyalty-card list's monthly send volume on the pricing page.