By default, all new Yahoo! email accounts do not allow access through username and password for 3rd party programs, like ours. Most accounts created before these updates have the “allow less secure” apps feature turned ON (so they are set to connect through username/password from 3rd party programs). Yahoo users are able to view and modify their setting on the Account security screen:

Yahoo considers using your email account through 3rd party programs, like ours, as ‘less secure’ for the reason of liability. But it is true that adding any 3rd party program to the mix, is always “less secure”, than simply using your Yahoo account directly and manually. So we actually recommend this : If you do not want to set your important Yahoo account to this lower security setting level, remember that you can simply create a new Yahoo account, just for the use with our software (for SMS and marketing only), in which account you will not have any sensitive data and do this setting for that account only.

In some cases, for some Yahoo domains and some Yahoo accounts, this feature is not available and you may have to go with a Gmail account. Remember both Yahoo and Gmail accounts are free to setup and use.