encode your username and password:
echo -en "<username>\0<username>\0<secret_password>" | base64-encode 0MKwtQ-1Dtkqj0oyz-00asfasdf
then connect to your provider using the telnet command:
telnet provider.com 25 >>Trying 123.123.123.123... >>Connected to provider.com >>220 Welcome to Nemesis ESMTP server on smtp.1und1.de HELO <domain> or <user@domain> or <your email> >>250 mrelayeu2.provider.com pleased to meet you AUTH PLAIN <your base64-encoded usernam/password-combination as mentioned above> >>235 authentication finished successfully Mail From: <your@email-address> >>250 mail from: <your@email-adress> ok RCPT To: <the@recipient-adress> >>250 <the@wrecipient-adress> ok Data >>354 Enter mail, end with "." on a line by itself this is your message, if you wand to send one, GNAGNAGNA . >>250 Message 0MKwtQ-1Dtkqj0oyz-0006Hy accepted by mrelayeu2.provider.com quit >>221 Bye