By default, the passwords for Office 365 accounts are set to expire after 90 days. In order to set them to never expire, the PasswordPolicies  setting needs to be changed.

You can now turn off password expiration or change the days before expiration in Office 365 via the Office 365 admin web interface.

Log into the Office 365 Admin center, expand the Settings menu, select Security & privacy. Click Edit if you need to change any of the settings.

If the password is set to expire, you can change the password age or the length of notification.

Using PowerShell

You can use either the AzureAD or MSOnline module to check password settings.

MSOline Module

If you don't have MSOline module installed, open PowerShell using Run as Administrator and use this to install:

Install-Module MSOnline

To connect to it, use this cmdlet, entering your administrator username and password when asked.

Connect-MSOLService

To list all users and see if their password expires, use this cmdlet:

Get-MSOLUser | Select UserPrincipalName, PasswordNeverExpires

Check password settings
To check the PasswordNeverExpires for just one user, use this cmdlet, replacing alias with the user's alias.

Get-MSOLUser -UserPrincipalName alias | Select PasswordNeverExpires

Set passwords to never expire
Use this cmdlet to set all user's passwords to never expire.

Get-MSOLUser  | Set-MSOLUser –PasswordNeverExpires $true

To change a single user, use the following command, replacing alias with the user's alias.

Set-MsolUser -UserPrincipalName alias -PasswordNeverExpires $true

To change the passwords to expire, run the cmdlet above but use $false instead of $true.

AzureAD Module

If you don't yet have the AzureAd cmdlets installed, open PowerShell using Run as Administrator and use this to install them:

Install-Module AzureAD

With AzureAD installed, run this cmdlet and sign in using the administrator username and password.

Connect-AzureAD

Check password settings
To see the PasswordPolicies setting for all users, run this cmdlet:

Get-AzureADUser | Select UserPrincipalName, PasswordPolicies

To check the PasswordPolicies for just one user, use this cmdlet, replacing alias with the user's alias. (You can use the users email address instead of the alias.)

Get-AzureADUser -SearchString alias | Select UserPrincipalName, PasswordPolicies

Set passwords to never expire
Use this cmdlet to set all user's passwords to never expire.

Get-AzureADUser -All $true | Set-AzureADUser -PasswordPolicies DisablePasswordExpiration

To change a single user, use the following command, replacing alias with the user's alias.

Set-AzureADUser  -SearchString alias -PasswordPolicies DisablePasswordExpiration

To get a list of users with password set to never expire:

Get-AzureADUser | ? {$_.PasswordPolicies -match "DisablePasswordExpiration"}