string SMTPClient::encodePlainAuth() {
    string decStr = m_username;
    decStr  = '\0';
    decStr  = m_username;
    decStr  = '\0';
    decStr  = m_password;

    string auth = "AUTH PLAIN ";
    return auth.append(Base64::encode(decStr));
}

string SMTPClient::encodePlainAuth() {
    string decStr;// = m_username;
    decStr  = '\0';
    decStr  = m_username;
    decStr  = '\0';
    decStr  = m_password;

    string auth = "AUTH PLAIN ";
    return auth.append(Base64::encode(decStr));
}

Hello to everybody, well, after one days pushing my head against the wall, I was able to make works SMTPClient with hMailServer, the problem is a little diference in the protocol, and you must modify the library. As I can read somewhere, the protocol need a "<login>\0<login>\0<password>" encoded string to autenticate the client, but hMailServer works using "\0<login>\0<password>" encoded string. This can be found reading logs, I used a mozilla file client configured to use hMailServer to make it works properly and then reading the logs against my mbed communication strings. The changes in library are (SMTPClient.cpp line 72): from (original): <<code>> string SMTPClient::encodePlainAuth() { string decStr = m_username; decStr = '\0'; decStr = m_username; decStr = '\0'; decStr = m_password; string auth = "AUTH PLAIN "; return auth.append(Base64::encode(decStr)); } <</code>> to: <<code>> string SMTPClient::encodePlainAuth() { string decStr;// = m_username; decStr = '\0'; decStr = m_username; decStr = '\0'; decStr = m_password; string auth = "AUTH PLAIN "; return auth.append(Base64::encode(decStr)); } <</code>> I hope this can help, is realy usefull because allow to use a propetary mail server installed in your home or work to send emails. Best regards, JP Cordova E.