Why You Should Stop Using Your @onmicrosoft.com Email Address
Have you ever received an email from a company using an @onmicrosoft.com address and thought, “That doesn’t look very professional”? You’re not alone. Many customers view these addresses as untrustworthy or even spam-like. Some organisations have seen better email deliverability and increased client trust simply by switching to a custom domain.
Microsoft is now taking steps to encourage this transition.
What’s Changing?
From mid-October 2025, Microsoft will begin limiting outbound emails from onmicrosoft.com domains to 100 messages per day per organisation. This change will be rolled out gradually and fully enforced by June 2026.
Although this might seem restrictive, it is actually a move towards a more professional, secure, and credible digital identity.
Why Microsoft Is Making This Change
Think of the @onmicrosoft.com domain like a temporary number plate. It is useful during setup, but never intended for long-term use. Microsoft wants organisations to adopt custom domains (such as yourcompany.com), and here’s why:
- Professional appearance – A custom domain shows clients and partners that you are serious.
- Trustworthiness – Recognisable domains inspire more confidence.
- Better deliverability – Custom domains build their own reputation, improving inbox placement.
- Greater control – You manage your identity, rather than relying on a placeholder.
Key Details
If your organisation still uses an @onmicrosoft.com address for external communication, here’s what to expect:
- Outbound email limit – 100 messages per 24 hours.
- Bounce-backs – Exceeding the limit will trigger a rejection (NDR code 550 5.7.236).
- Internal email – This change does not affect internal communication.
- Rollout timeline – Begins October 2025 and completes by June 2026.
How to Prepare
Switching to a custom domain is straightforward. Here’s a quick guide:
- Audit usage – Use Message Trace in the Exchange Admin Centre.
- Set up your domain – Purchase and configure it in Microsoft 365.
- Make it the default – Ensure new users are assigned the custom domain.
- Update existing users – Change their primary email addresses.
- Reconfigure apps – Update services like Microsoft Bookings or automated notifications.
Compliance and Continuity
This change does not affect compliance features, but it does require attention. Applications or services tied to @onmicrosoft.com addresses may stop working if not updated. Administrators should monitor usage to avoid disruption.
Final Thoughts
This is not just about Microsoft enforcing a limit. It is about helping organisations evolve. A custom domain enhances trust, security, and brand consistency. It is a small change that can make a big difference.
Take a moment today to check your Microsoft 365 Admin Centre. If you are still using an @onmicrosoft.com address, now is the time to upgrade.