Hybrid Mailbox Sending Limit

Copper Contributor


Dear all,

I hope you're all having a good day. Today, I'd like to discuss the sending limit for Exchange hybrid mailboxes.

Before we delve into the topic, let me explain my current infrastructure and the pain points I'm facing:


I'm running a Hybrid Exchange Server 2019 setup where the MX record is pointed to Exchange Online Protection (EOP). Additionally, I have one email address designated for SMTP relay, which an application utilizes for sending emails via SMTP relay. This mailbox resides on our on-premises Exchange servers.


The issue I'm encountering is when we need to send around 200,000 emails at the end of every month. When we reach the 100,000 mark, EOP restricts that account from sending any more emails. How can I solve this problem?

Looking forward to your insights and suggestions.


Suraj Verma 

1 Reply

EXO is in principle not meant for bulk mailing to external recipients. You have three options:

1) Have Exchange on-prem (Hybrid) send directly to external recipients

2) Use multiple accounts when sending (authentication)

3) See if the app can leverage Azure Communication Services for bulk mail - see https://learn.microsoft.com/azure/communication-services/overview


While some things are "tolerated" at the moment, the recently announced HVE article provides pointers to where things are going, see https://techcommunity.microsoft.com/t5/exchange-team-blog/public-preview-high-volume-email-for-micro...