1 TurboSMTP
TurboSMTP is a user-friendly and reliable SMTP server that guarantees a controlled IP and maximizes the deliverability of your direct email marketing, transactional emails, marketing campaigns, and bulk email sends.
2 SendGrid
SendGrid is a leading cloud-based email infrastructure that blends transactional email, email marketing, and SMTP features in a famous API company. It's not easy to determine which is the SendGrid main area of expertise.
3 SMTP2Go
SMTP2GO is a popular SMTP service which promises to "remove the headaches of email delivery, saving you time and money", and it keeps promises.
4 SparkPost
SparkPost is one of the new players in the SMTP and transactional email service market. Born in 2014, it became popular quickly and recently took advantage of the user migration from Mandrill.
5 AuthSMTP
AuthSMTP is another little known but good outgoing SMTP email service that can be used to send emails from any software, service, device and application can authenticate with a username and password.