Problem changing password on ODK Central

I have just installed ODK CENTRAL, everything works fine.
I have added 2 users but I can't change their passwords and the password reset service doesn't send any message to the 2 users' emails. Someone can help for this problem

Are you using the default email server that comes packaged with Central or are you using a 3rd party service like Mailjet? If you are using the default email server, the docs describe why the emails may not be delivered: