High Volume Email for Microsoft 365 Preview: Unlocking Email Potential

Microsoft has introduced the public preview of High Volume Email for Microsoft 365. HVE is a specialized service tailored for line of business applications and other high-volume SMTP Auth submissions, allowing you to send internal messages beyond the current limits of Exchange Online. This service is particularly beneficial for customers using on-premises servers in an Exchange hybrid setup, enabling them to transition to HVE and retire their on-premises servers.

The rollout of HVE to all worldwide customers will commence on April 1, with completion expected by the end of April. Initially, the HVE endpoint will be based in the North America region, with plans for additional regions to be launched in the coming months.

Our objectives with High Volume Email for Microsoft 365 are multi-fold

• Enable customers to send larger volumes of email than conventional user mailboxes, particularly to internal recipients, without recipient rate limits.
• Provide a solution for high volumes of external email through Azure Communication Services.
• Empower administrators to set custom limits on a per-account basis and offer a consumption-based billing model along with usage metrics and tracking.

Beyond the constraints of typical mailbox limits, HVE meets the evolving needs of email usage, supporting scenarios such as communication from hardware devices and mass email from line of business applications within Exchange Online.

Exchange Online currently imposes outbound limits on email sending based on Recipient Rate and Message Rate. HVE breaks through these limits, employing a transactional model based on the number of emails sent. During the public preview, usage will be free, limited to 100,000 recipients per day per tenant. These limits will be expanded upon General Availability, with tenant admins gaining the ability to set volume thresholds on a per-account basis for enhanced control over volume and costs.

Recipient rate limits are put in place to deter the sending and delivery of unsolicited bulk messages. Currently, all licenses highlighted in green maintain a recipient rate limit of 10,000 recipients per day per user for both outbound and internal messages. However, during the Preview phase of HVE, the recipient limit is raised to 100,000 recipients per day per tenant and will expand further at General Availability (GA). It’s important to note that HVE limits are distinct and not cumulative with the green-highlighted limits.

Message rate limits dictate how many messages a user can send via SMTP from Exchange Online within a defined timeframe. If outbound message volumes exceed the message rate limit, any surplus in message submissions will be throttled and gradually processed in subsequent minutes.

Public Preview Details of High Volume Email for Microsoft 365

HVE allows you to create MailUsers (up to 20 during the preview phase) in Exchange Online, enabling them to send messages using a designated SMTP endpoint.

The public preview features an administrative interface within the Exchange admin center to manage HVE accounts, a comprehensive usage report, and an SMTP endpoint that utilizes basic SMTP authentication for sending emails.

Limits during the public preview will expand at GA.

Feature	Max Number Per Tenant
HVE Accounts	20
Recipient rate limits	100,000 per day (per tenant)
External recipients	2,000 per day (per account)

Service Information of HVE

• Server/Endpoint: smtp-hve.office365.com
• Port: 587
• TLS: STARTTLS
  TLS 1.2 and TLS 1.3 are supported
• Authentication: Username and password

Authentication for High Volume Email (HVE) in Microsoft 365

During the Preview phase, High Volume Email (HVE) for Microsoft 365 requires SMTP Basic Authentication. However, upon reaching General Availability (GA), OAuth authentication is anticipated to be supported.

Here are a few additional details regarding authentication for HVE:

• If Security Defaults are enabled, all basic authentication methods, including SMTP, are disabled, rendering HVE non-functional.
• HVE accounts can continue to operate even if SMTPClientAuthenticationDisabled is set to True within TransportConfig, thanks to the utilization of a custom endpoint.
• To avoid any disruptions caused by authentication policies, customers should ensure that AllowBasicAuthSmtp is enabled in the policy applicable to the HVE account. Custom authentication policies can be implemented for HVE accounts as needed.

Conclusion

The public preview of High Volume Email (HVE) for Microsoft 365 presents a promising solution for businesses seeking to expand their email capabilities beyond standard limits. With HVE, organizations can send internal messages at significantly higher volumes, leveraging SMTP Basic Authentication during the preview phase and anticipating OAuth support upon General Availability. Despite potential authentication challenges with Security Defaults, HVE accounts can remain operational through custom endpoints and appropriate policy configurations. As this innovative service progresses towards widespread adoption, it offers enhanced flexibility and scalability for managing email communications within Exchange Online, catering to diverse business needs effectively.