My account keeps being locked when I send out emails to groups

This usually happens because the account is being flagged for unusual or spam-like sending activity. Microsoft accounts can be locked when activity might violate the Terms of Use, and sending to many people at the same time can trigger that protection even on an older account.

What to do:

1. Try to unlock the account at https://account.microsoft.com.
2. If Outlook.com says the account is temporarily blocked because of unusual sign-in activity, reset the password to unblock it.
3. If the sign-in flow does not show Let’s prove you’re human, use the aka.ms/ link shown in the lock window and submit the account reinstatement form.
4. After submitting that form, do not submit additional requests, because that can slow the review.
5. Once access is restored, reduce the chance of another lock by avoiding large group sends at one time and sending to smaller sub-groups instead.

Also check whether the mailbox or OneDrive storage is full, because a full mailbox or storage can prevent sending and receiving.

If the account was compromised or started sending spam, secure it by changing the password and reviewing recent account activity.

References:

• Microsoft account has been locked | Microsoft Support
• Unblock my Outlook.com account | Microsoft Support
• Bulk Outlook email blocked and restricted for 24 hours - Microsoft Q&A
• How to stop my Outlook email from sending spam messages, as my emails are not being delivered - Microsoft Q&A