We are planning to implement Yahoo email client same as other clients like Thunderbird , Out look etc.
In some of your yahoo forum posts users reported that same message is getting assigned with different message ID's on different dates

Please look into this forum post http://developer.yahoo.com/forum/Yahoo-Mail-Web-Services-API/How-to-uniquely-identify-an-email-/1317083060065-b561ded1-d2fa-4cb5-b3d1-112107d0743c

If message ID changes then Is there any other way to uniquely identifying the message. How clients sync for deleted emails by relying on this type of message ID's.

Please help us here