the account might be anonymous but you aren't. mail not read as web mail has internet headers including your IP address. if you have a static IP thats it.
i have traced emails sent to me via yahoo france to a dial-up in tunis tunisia eg. the scammer attempted to provoke me as an american during the recent war by writing various requests to me and signing as bin laden. he got my address from a more public bbs than this one.
i suppose you could use an internet proxy and secure tunneling. even that leaves electronic fingerprints.
pi