Sending mail failed: SMTP protocol error

[Merciadri Luca]

Hello,

I am encountering an error either when sending mail or when posting on
Usenet.
Gnus tells me ``Sending mail failed: SMTP protocol error.'' I do not
understand the reason of such a message, as my credentials are
available for it.

When sending a mail to somebody, Gnus first tries to send it using
``SMTP,'' but it always results in this error. When trying a second
time, it says ``Sending via mail...'' and the mail is sent (and
correctly received).

However, it never works for Usenet groups.

Why?


Thanks.