The easy way would be like this:

message.getFrom()[ 0 ].getString(), because I really don't know how there could be more senders than one.

The nicer way would be:

Address[] senders = message.getFrom();
for ( int i = 0 ; i < senders.length ; i++ ) {
  // identification lets you use more methods in case of InternetAddress
  if ( senders[ i ] instanceof InternetAddress ) {
    ( ( InternetAddress ) senders[ i ] ).toUnicodeString() ;
  } else {
    senders[ i ].toString() ;
  }
}