Microsoft Outlook 2016 and Outlook.com Email Address - Microsoft Community

i added outlook premium account , setup personal domain name me, wife , dog.  yes dog has own email account therapy dog , works lot of events @ local hospitals , children's homes, , it's great have separate account manage these events. 

the setup when 3 accounts , able log 3 via webmail, , able to add them mobile phones , our home computer via microsoft outlook 2016 running windows 10.  accounts me , wife have been working fine several days , enjoy service.  account dog worked less 18 hours then the microsoft outlook 2016 software came login error requesting password.  password can entered, remember credentials checked, , still comes right within 10 seconds.  this account not syncing on microsoft outlook 2016 software.  continues work via webmail , via mobile phone app.  know it's right password can log account via web service.  account removed , reloaded microsoft outlook 2016 software no change. 

background:  not sure if has during creation of accounts requested provide name , age.  in the dogs case 7 years old kicked in requirement of adult parent consent account creation , forced pay $0.50 via credit card.  performed , account setup , worked fine 18 hours. 

i'm open suggestions.

is 'dog's' mail account using 2 step verification?

if when starting ol hold ctrl key force safe mode, a/c function?

Office / Outlook / Windows 10 / Office 2016