Find the odd term 1-yahoo 2-msn 3-smtp 4-rediff

3- SMTP - it is just a protocol 

Yahoo: Yet Another Hierarchical Officious Oracle

MSN: Microsoft Network

SMTP: Simple Mail Transfer Protocol

Rediff: Translation from Hindi meaning >> Near by words

I personally see the last one as the odd one, but again, maybe that's cos I'm used to the first 3 terms more than the last. They've been around for too long now that they became known to all at some point of time.

Again, this is a personal opinion. Someone else may say the 1st and 4th are odd since their meaning is not related to computers.

Thanks for the invite, I leave the answer to experts who specialize in this area