Not sending group invite.

Hello,

Is this a free account? A free Outlook.com account, especially a brand-new one, may have a very low daily sending limit. Sending to a group of 90 in one email counts as 90 emails sent. The sending limit for Outlook.com and Hotmail accounts works somewhat like a credit score. Each account may have a different limit depending on factors such as the account’s age, sending history, usage patterns, reputation, and whether it is a free or paid account.

Microsoft explains the sending limits and ways to improve the account’s reputation here:

https://support.microsoft.com/outlook/sending-limits-in-outlook-com

Unfortunately, even if you follow all of Microsoft’s recommendations, the sending limit will not increase overnight. The account needs time to build a normal and trusted sending history. Unfortunately sending to a group of recipients will not help and can be often flagged as spamming activity.

This is also not limited to Microsoft. Gmail and other email providers have introduced similar restrictions to combat spam and prevent newly created accounts from sending large numbers of messages.