How to test smtp email with DOS, not telnet?

I know how to test smtp email using telnet. But I think because telnet uses "its own channel" to reach smtp server, it doesn't necessarily mean the normal smtp communication on port 25 would work. (Please correct me if this is not true)

Basically the client has encountered with an issue : [ERROR] Access to default session denied during a test from application to reach smtp server. From the same server, telnet to send an email just works...

So I've got no other choice but to figure out why I am getting this sort of error. Done my research only to find out lots and lots of command-line email applications, no good in this case as it is the client's env开发者_JAVA百科ironment that I've got little control on what to install.

So I think the last resort would be using simple DOS commands? Please advise if there is even a better way. Many thanks in advance.

I know how to test smtp email using telnet. But I think because telnet uses "its own channel" to reach smtp server, it doesn't necessarily mean the normal smtp communication on port 25 would work.

That's incorrect. If sending e-mail works with typing it to the Windows telnet application, then it works, i.e. there is no problem with the SMTP server, and there are no firewall issues between the client and the server.

So the bug is most probably in the in the application displaying the error message. Maybe there is no bug, but the application is not configured properly.

I think because telnet uses "its own channel" to reach smtp server, it doesn't necessarily mean the normal smtp communication on port 25 would work. (Please correct me if this is not true)

That is not true. A "real" SMTP client uses the same method to talk to the SMTP server as telnet does.

If you do not trust Telnet, use Thunderbird, but the problem is probably with your client software or configuration. Double check the settings there and see if you can turn on any trace logging (on the client or the server).