SMTP Prober is a portable tool which makes it easy to test particular SMTP settings to confirm that they'll allow you to send emails.

Essentially the program works like a miniature email client. So you can enter details like your host address, user name, password and port number, as well as message-related information (To, CC, BCC, From, Reply To, Subject, Body etc), only all in a single screen.

When you're ready, click the Send Email button.

And in a moment you'll get a response in the "Result" box. Which might be, say a "Host not found" error if you've specified the wrong server address, but will hopefully be "Email sent" if you've got everything right. (Although you'll need a real email client to check the destination account and confirm that the message has been received correctly.)

It's all fairly basic, but if you're getting SMTP-related errors somewhere then SMTP Prober may help you figure out why, and it's certainly convenient to use: the program comes in a single executable which is also portable, no installation required.