If you are sending to 3,000+ recipients using individual tracking, you may notice sending takes a while or may stop your Outlook altogether. This is because Microsoft has sending limits for each email address.
To solve this, ContactMonkey launched Email at Scale. This feature allows you to send to over 10,000 recipients at a fraction of the speed. Reach out to your account manager for next steps.
Note that this is available for Office 365 and Gmail customers.