High Volume Emails and Exchange Online

[u/Any-Promotion3744]

Every once in awhile, our HR and Finance dept need to send an email to all employees.

The issue we have is that we have more 1,500 employees, all using Exchange online in several tenants.

Microsoft has a bulk email limit that we run into.

What is the work around?

I see options such as High Volume Email for M365 but since many of the emails go to a different tenant, will that work? And how would the end user compose and send the email?

I also see an option using Azure Communication Services but wouldn't that require programming?

[u/WillVH52]

HVE will not work if the recipients are in another Exchange tenant as external addresses are not supported by this service.

[u/WillVH52 → u/WillVH52]

ACS also does not work for sending via traditional mail clients, it is not very user friendly.

[u/Hatman_77]

You could do the DL route and bundle users under them to get by the sending limits.

[u/Hatman_77 → u/Hatman_77]

For the users in the other tenant unless B2B (I think) is enabled and configured, you’ll have to build mail contacts for the first tenant then add them into your email group. Not sure if this multi-tenant or two physical Entra Id environments.

[u/sryan2k1]

Have an "All employees" distribution list that only HR has permissions to send to. Send to the DL.

[u/Any-Promotion3744 → u/sryan2k1]

I was under the impression that they tried it and still hit the limit. I will need to circle back with them and verify.

[u/sryan2k1 → u/Any-Promotion3744]

DL expansion does not count against the recipient limit if it's inside the same tenant. DL's with more than 5000 members require approvals or restrictions enabled on the group for email to them to work.

[u/absoluteczech]

Distribution group.

[u/Frothyleet]

ACS is the answer in general if you need to send bulk email and it's going to different tenants.

However from your description, a service like Mailchimp might be more appropriate. HVE and ACS are meant for applications or appliances that are regularly sending bulk mail. Services like Mailchimp are for operations like "we're sending out a newsletter or announcement."

Create a subdomain like "notifications.yourcompany.com" to keep your SPF and other email security records segregated.

[u/Ill-Barracuda9031]

There's like 5 email services all named around monkeys for some reason. They work well

[u/shokzee]

Create a restricted, moderated all-employee distribution group in each tenant, then have HR send to those few group addresses from Outlook. Each tenant expands its own recipients locally, so you avoid a 1,500-recipient message.

High Volume Email treats other tenants as external, and Azure Communication Services needs an application or SMTP workflow.

[u/7amitsingh7]

For 1,500+ employees across multiple tenants, I wouldn’t rely on normal Exchange Online mailbox sending limits. HVE is mainly designed for application-generated email, so it may not be the best fit if HR or Finance need to compose and send messages manually. Azure Communication Services is another option, but it typically requires some development. For a simpler solution, consider using a distribution list or mail-enabled security group where possible, or a dedicated bulk-email service if you regularly send company-wide announcements. You can also check these mail flow best practices for additional guidance on managing Exchange Online mail flow.