As both a security precaution and a way to effectively utilize system resources, Microsoft Exchange only allows emails to be sent to 10,000 recipients per day by a single user. If this number is exceeded, the system will automatically disable the sender's email for 24 hours. This can easily be avoided using the following strategies:
- Break up the communications over several days.
- Use a distribution group, if possible. A distribution group counts as one "recipient" and will go a long way when it comes to keeping you under the limit.
If this severely impacts despite the workarounds, please reach out to T&I with details regarding your workflow.
Please also remember to use BCC for recipients when sending to large groups so that recipient email addresses are not visible to the other recipients.
For more information on Microsoft Exchange limits, visit their page.