Smtp server which expect SSL connection on 465 or 587

Question

有一些使用端口465进行安全连接的SMTP服务器，但是，当使用TcpClient连接到该端口上的这些服务器时，没有发送欢迎消息，请问我在连接后立即确保连接的安全吗？

Answer 1

465 is meant for STMP over SSL, you'll have to establish an SSL connection before the SMTP conversation even starts, otherwise you won't get anything back, including a greeting banner. TLS works differently by starting a conversation and then encrypting.