Do emails from yahoo/gmail etc. constitute valid evidence in

Yes, you need to get authenticated the email from Expert

thanks for your help, who are these experts we are talking about. can you provide me with some details ...

yes they can be used as evidence in th court.  You can take the print out of the mail and can produce it in the court.  To prove that you will have to call the concerned person of the domains.  I have not come across the judgments yet.

Will agency like IFS INDIA or others like this be able to help in authenticating these emails?

SMS and emails are accepted. Day in and day out we read that the senders of obnoxious and threatening messages are being caught and produced before the court. If they are not evidence, what the court will do?

It is like any other mail. Although I have not read or heard any where that email is accepted as evidence, still I know one thing for sure that that it is an authentic medium of communication and accepted as genuine. I have personally presented a series of communication made through email, as evidence in Arbitration court, and the same has been accepted by the Arbitrator. 

All printouts from the electronics media like FAX, TELEX, Telegram, e-mail, photographs, written communication etc. are admissible as evidence. We are living in the cyber age. E-mails come with the thread and date, time etc. so they are self-explanatory. Even mobile talk or photos are admissible. Now video-conferencing and evidence would become a legal reality.

There are N number of cases decided on the basis of such evidence. You need not suspect the legal validity. Go ahead with whatever you may have to do with such evidences in any court or outside.