FoxMails has free IP based Email services and with foxmails tool send upto 10000 emails per day with each user.
Issues with Email Delivery?
(1) You sent too many spam emails and the blacklist monitor marked your user IP as spam.
(2) Some of email domain has very hard level of spam filter, you can check your email content to fix that.
(3) Your Login credential is using by more than one user. please note: only one active user allowed.
(4) Your ISP might be blocking your port 25 for outgoing email, in this case use VPN for your IP security.