I think Gmail is the first webmail provider that features the Conversation -- having only one mailbox entry for messages in the same thread. Neat.However, a downside to this is that when you edit the subject just a wee bit (even just one character), that new message breaks apart from the rest of the Conversation and itself creates a new thread. Yes, changing the subject does have its benefits.Can I put together several related messages into one Conversation?
Put together several messages into one conversation in Gmail
gmail;gmail conversations
This is by design, so it is not possible. There is no mechanism to merge conversations and the only way to split a conversation is to change the subject, even if it's only one character.