Starting on October 15, 2025, Microsoft is implementing new rules that will limit the number of external emails sent from its default “onmicrosoft” domains. These domains, which are also known as MOERA (Microsoft Online Email Routing Address) domains, are shared among different tenants. The change, which will roll out gradually through 2026, will cap outbound emails at 100 external recipients per day for each organization. It’s important to note that this policy change will not affect incoming mail.
The primary reason for this new restriction is to protect the reputation of these shared domains. Spammers and malicious actors often exploit these free domains to send fraudulent emails. This can harm the deliverability of legitimate mail and tarnish the collective reputation of all users on the same shared domain. To address this, Microsoft is actively encouraging organizations to switch to a custom domain.
Migrating to a custom domain offers several significant benefits:
- Improved Security: Using a custom domain enhances your organization’s email security.
- Better Deliverability: Emails sent from a custom domain are more likely to reach their intended recipients without being flagged as spam.
- Stronger Brand Identity: A custom domain reinforces your brand’s professionalism and credibility.
To successfully migrate, organizations should follow these steps:
- Purchase a custom domain: Acquire a domain name that aligns with your brand.
- Add it to Microsoft 365: Follow Microsoft’s guidelines to add the new domain to your account.
- Update user mailboxes: Change user email addresses to the new custom domain.
- Configure applications: Adjust any applications or services to send emails from the new domain.
In summary, while the onmicrosoft domains remain useful for internal communication and testing purposes, they are no longer an ideal solution for regular external business communication due to the new restrictions and the potential for a diminished sender reputation.
If you would like professional help to ensure your email systems are setup securely and for maximum deliverability, contact CORE Networks today…
