Hi,
Are you able to sign in to your account normally without any security alerts?
This usually happens when activity is flagged as unusual, like reporting many emails quickly, so go to your account security page, review recent activity, and confirm it was you, then complete any verification steps if prompted, next sign out of all sessions and sign back in, and if the block remains, use the “Too many messages sent” recovery form or wait 24 hours for the limit to reset.
These steps will clear the restriction and confirm your account is safe.