How can I send two emails via javamail such that outlook will put them in the same conversation?

At some point, I've sent an email and it is processed and received by an exchange server and then viewed by an outlook client. At a later point, I send another email where it is a reply/related to the 1st email. I want outlook to know that they are related and group them together when I group emails by conversation.

A couple of caveat开发者_StackOverflow中文版s:

1. I won't have access to the 1st email's message object to reply off of.
2. I will have the subject, messageID, and body of the first email when composing the 2nd email.

I've tried adding the "in-reply-to" and "references" header fields in the 2nd email, but outlook will not conversate them. Thunderbird and Gmail will thread them appropriately, though.

When grouping messages into a Conversation, Outlook will most likely not use the header fields but rather the subject line. It will ignore words like Fw: and Re:.

Try prepend a Re: to the first message subject and use this as second message subject.

Ref: http://lifehacker.com/157042/make-outlook-thread-conversations-like-gmail