To help protect against abuse by spammers, Outlook.com limits the number of email messages that you can send in a single day, as well as the number of recipients for a single message. For each person, Outlook.com calculates a sender “reputation”, which is based on a number of factors, including how long that person has had their account and whether recipients of their past email messages marked those messages as spam. These reputation-based limits can change depending on the volume and type of ongoing spammer attacks.
You can purchase an Office 365 Home or Office 365 Personal subscription to get a higher limit for messages you send. Spammers are not generally willing to cover a subscription cost, which allows our paid limits to be higher. The limits for Office 365 Home or Office 365 Personal subscribers are:
Daily recipients: 5,000
Maximum recipients per message: 500
Daily non-relationship recipients: 2,000
A “non-relationship recipient” is someone you've never sent email to before. If you need to send more email messages per day than the limits shown above, we recommend that you use a third-party bulk email provider like SendGrid, ExactTarget, or ConstantContact.