Hacker always come up with innovative ideas to hack email ids. Fake sms and email bomber softwares are one of them. Now let us have a look at how this sms and email bombers are used to hack email ids on a large scale. So what the hacker will do is, make a simple program with Graphical user interface using programing language like Visual Basic or Java (This basic programs are very easy to make if you have some knowledge of Visual Basic). The GUI is kept very basic with minimum options. Now when the user fills the fields and presses "bomb" instead of doing its said work it will just deposit the username and the password in the hackers database and give the users some silly error like "Server busy" or "The target has blocked you" etc. So don't be surprised when you receive a email about Viagra or Porn sites because after collecting enough of this email ids the hacker will just sell them to site owners.
I am not saying that all this softwares are fake, there are some genuine software which really work.But they have their limitations. Do you really think that Gmail will allow anybody to bomb anybody? It will quickly understand your intentions and stop you.
So next time if the thought of bombing comes in your mind. Just pause for a minute and think, do you really want to do this? my personal opinion about bombing is that it is very childish and immature and if anybody gets satisfaction or happiness by doing such dumb things then he should get some psychological help.