I have received an email from a friend with a yahoo account. My email is with my service provider sify. My mail contained the following information

domainkeys has found that the mail has been tampered

Can anyone explain this to me, have sify been intercepting my mail?
The warning originates with yahoo so I do not think it would be them tampering with my mail but as I am not that familiar with internet things I just dont know.
Thanks

Domainkeys is a method adopted recently by various service provider to make sure that mail is not spoofing.

You are receiving this error most probably as it suspect that mail is sent from another domain but its showing that its from different domain.

eg. .. may be mail is sent from "xyz.com" domain but you are seeing that mail is from "abc.com" so this error is there.

If you can post full header info here then I can tell you bit more!