Are you using the Azure Active Directory service? To increase the security of your account, Microsoft has now increased the character limit of your cloud based Azure Active Directory password.
With this rule in place, you can now configure a password for your Active Directory with much more flexibility, while keeping your account secure.
As a security measure to your Azure Active Directory, Microsoft has now increased the character limit of AD password to 256 characters. This is definitely a significant increase from the previous 16 characters limit.
You can use alphabets (lowercase, uppercase), numerics, special characters and blank spaces to form your AD (Active Directory) password which will add additional security to your online account. Microsoft has detailed about it on their password policies documentation page.
This new change will be applicable only to the Active Directory users. The Microsoft accounts (MSA) which meant for personal use won't get this rule imposed yet.