是javax.mail爲每個郵件使用兩個smtp會話嗎？

Question

所以我們正在調試一些網絡問題，發送郵件需要5秒鐘，從telnet到smptp服務器。使用javax.mail發送郵件的問題是需要10秒鐘......我們已經打開了javax.mail中的日誌記錄，它看起來像打開了兩個smtp會話，並且第一個不會發送任何數據。這可能是因爲5秒的延遲？某種超時？或者這是如何javax.mail的作品？

我們的郵件代碼：

Properties props = new Properties(); 
props.put("mail.smtp.host", _smtpHost); 
Session session = Session.getDefaultInstance(props, null); 

session.setDebug(true); 

Message newMessage = new MimeMessage(session);   
newMessage.setFrom(new InternetAddress(from)); 
newMessage.setRecipient(Message.RecipientType.TO, new InternetAddress(to)); 

newMessage.setSubject(subject); 
newMessage.setSentDate(sentDate);  
newMessage.setContent(content, contenttype); 

Transport transport = session.getTransport(SMTP_MAIL); 
transport.connect(_smtpHost, _user, _password); 
Transport.send(newMessage); 

調試輸出：

DEBUG: setDebug: JavaMail version 1.4ea 
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Sun Microsystems, Inc] 
DEBUG SMTP: useEhlo true, useAuth false 
DEBUG SMTP: trying to connect to host "mail.xxx.xxx", port 25, isSSL false 
220 mail.xxx.xxx ESMTP Service (Lotus Domino XXX) ready at Mon, 7 Nov 2011 09:15:00 +0100 
DEBUG SMTP: connected to host "mail.xxx.xxx", port: 25 

EHLO MYCOMPUTER 
250-mail.xxx.xxx Hello MYCOMPUTER ([10.xxx.xxx.xxx]), pleased to meet you 
250-HELP 
250-VRFY 
250-EXPN 
250-DSN 
250-SIZE 256000000 
250-8BITMIME 
250 PIPELINING 
DEBUG SMTP: Found extension "HELP", arg "" 
DEBUG SMTP: Found extension "VRFY", arg "" 
DEBUG SMTP: Found extension "EXPN", arg "" 
DEBUG SMTP: Found extension "DSN", arg "" 
DEBUG SMTP: Found extension "SIZE", arg "256000000" 
DEBUG SMTP: Found extension "8BITMIME", arg "" 
DEBUG SMTP: Found extension "PIPELINING", arg "" 
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Sun Microsystems, Inc] 
DEBUG SMTP: useEhlo true, useAuth false 
DEBUG SMTP: trying to connect to host "mail.xxx.xxx", port 25, isSSL false 
220 mail.xxx.xxx ESMTP Service (Lotus Domino XXX) ready at Mon, 7 Nov 2011 09:15:05 +0100 
DEBUG SMTP: connected to host "mail.xxx.xxx", port: 25 

EHLO MYCOMPUTER 
250-mail.xxx.xxx Hello MYCOMPUTER ([10.xxx.xxx.xxx]), pleased to meet you 
250-HELP 
250-VRFY 
250-EXPN 
250-DSN 
250-SIZE 256000000 
250-8BITMIME 
250 PIPELINING 
DEBUG SMTP: Found extension "HELP", arg "" 
DEBUG SMTP: Found extension "VRFY", arg "" 
DEBUG SMTP: Found extension "EXPN", arg "" 
DEBUG SMTP: Found extension "DSN", arg "" 
DEBUG SMTP: Found extension "SIZE", arg "256000000" 
DEBUG SMTP: Found extension "8BITMIME", arg "" 
DEBUG SMTP: Found extension "PIPELINING", arg "" 
DEBUG SMTP: use8bit false 
MAIL FROM:<tommy@xxx.xxx> 
250 tommy@xxx.xxx... Sender OK 
RCPT TO:<tommy@xxx.xxx> 
250 tommy@xxx.xxx... Recipient OK 
DEBUG SMTP: Verified Addresses 
DEBUG SMTP: tommy@xxx.xxx 
DATA 
354 Enter message, end with "." on a line by itself 
Date: Mon, 7 Nov 2011 09:14:55 +0100 (CET) 
From: tommy@xxx.xxx 
To: tommy@xxx.xxx 
Message-ID: <145229992.01320653699737.JavaMail.XXX@MYCOMPUTER> 
Subject: Test av html-mail 
MIME-Version: 1.0 
Content-Type: text/html; charset=UTF-8 
Content-Transfer-Encoding: 7bit 
sending myself an email... 
250 Message accepted for delivery 
QUIT 
221 xxx.xxx.com SMTP Service closing transmission channel 

Answer 1

javax.mail不使用任何 Telnet會話。它使用POP3或SMTP會話。