Are all accounts using the same server name, the same ports and the same authentication mechanism (should be OAuth2 these days) on both PCs? If that is not the case, please replicate the settings of the accounts that work to the accounts that do not work. My assumption would be that the configurations on the PC are of different age and that the mail accounts have been set up at a time where other server configuration settings were to be used compared to what is required today. Google (as well as Microsoft) are moving away from password based authentication for email and request OAuth2 so it is likely they recently deactivated passwords on the servers hosting your accounts. Please advise if this is getting you you anywhere.