Download SMTP Dialog
If you want to test an SMTP connection then this is one of the best available software. The SMTP Dialog lets you test secure authentication and SMTP. It is better than raw telnet to port 25. It provides an easy to use interface but very effective in action.
It comes with various options including: DATA, RCPT TO, EHLO or HELLO, MAIL FROM, NTLM, . Secure SMTP with STARTTLS.
The software is available for free to download. You can download and use the complete version for free of cost. The file is very small in size at only 18.33 KB and very easy to run.