# What are the maximum limits for mail merge campaigns?

> Discover the recipient limits and sending constraints for SecureMailMerge campaigns in Outlook, including maximum emails and campaign size.

SecureMailMerge does not impose any artificial limits on the number of recipients you can include in a mail merge campaign. However, there are some practical considerations:

## Microsoft 365 Sending Limits

Your sending limits are determined by your Microsoft 365 subscription and tenant configuration:

- **Microsoft 365 Business**: Typically 10,000 recipients per day
- **Exchange Online**: Usually 10,000 recipients per day with a maximum of 500 recipients per message

These limits are enforced by Microsoft, not SecureMailMerge. Your IT administrator may be able to adjust some of these limits for your organization - contact them if you need higher limits. For a full breakdown of the limits, the error messages you see when you exceed them, and pacing strategies, see [Outlook email sending limits](https://www.securemailmerge.com/knowledge/outlook-email-sending-limits/).

## Setting your own daily limit

SecureMailMerge can also enforce a limit you choose yourself. In the advanced options, under **"Schedule"** and then **"When to send"**, tick ["Limit how many are sent each day"](https://www.securemailmerge.com/help/sending-mail-merge-during-specific-hours/) and set the number of messages per day (ticking it fills in 50). No more than that many messages are scheduled per calendar day, and the rest move to the next selected sending day.

This is the simplest way to stay well below Microsoft's caps on a large campaign. You can combine it with a daily time window and a weekday selection on the same screen.

![The daily message limit in the When to send subgroup](https://www.securemailmerge.com/screenshots/advanced-options-schedule-when.png)

## Attachment Size Limits

The default message size limit in Microsoft 365 is 35 MB (including attachments). Administrators can increase this up to 150 MB. Keep in mind that attachments grow by about a third when sent via email, so a 24 MB file actually uses around 32 MB of your limit.

For large files, consider sharing via OneDrive or SharePoint links instead of direct attachments.