OK, can't make a headway now. I send the EHLO command to the SMTP server and get a reply that says AUTH LOGIN and AUTH PLAIN are supported. There are other methods, like CRAM-MD5, but I think that's something to do with SSL or such other encryption.

I try the AUTH PLAIN command. The server responds with 334 Go On. That means the AUTH PLAIN command was acknowledged by the SMTP server. Now what? How do I proceed?

I created a dummy SMTP server and ran my Outlook Express with it. OE sent the EHLO command and I imitated the server response I had received earlier. OE simply proceeded with the MAIL FROM command.

Then I adopted the same approach with my own SMTP code, and when the server returned 334 Go On after I had sent AUTH PLAIN, I tried sending the MAIL FROM command, but the server then returns with AUTHENTICATION FAILED message.

I am testing the code in this way: I try to send various possible commands to my SMTP server. Whenever I am stuck at some response, I use my SMTP server code to imitate these responses with my Outlook Express as the client. Whatever steps OE takes, I repeat them with my SMTP code. So far I don't seem to be able to authorize the SMTP transaction the way OE does. Any help?

I am using the GMX mail service for this purpose. My OE settings for SMTP are simple authorization with the same username and password as the POP settings. No SSL etc. And OE works perfect with the GMX account. The SMTP server is mail.gmx.net.

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