[YLUG] mail client for easy multiple identities

[Mark]

Hi,

I like to give the different organisations that I deal with different
email addresses, so I know who spams/sells on etc.   
I have a couple of domains and just give out addresses as I like, so
ylug at ...  etc.

What I am looking for is a mail client that will let me just put
whatever I want in to the from field, rather than have to set up
specific identities.

Anyone know of a suitable product?  

thanks

MArk