Why indefinite loop is not working in Gmail forwarding?

Question

I have created 2 new mail-id's,

nullable1@gmail.com

nullable2@gmail.com

And I created a filter in both mail-ids, So as to forward the nullable2's incoming mail to nullable1 and vice versa.

And I manually composed a new mail in nullable1 and forward to nullable2.

And What I expected is, an indefinite looping will set between nullable1 and nullable2 , and so my both mail's inbox will always be busy.

But that was not happened.

After sending the mail,

CASE 1: If I click on inbox link in left pane, only one mail was transferred to nullable2. And I can see the sent mail as a single mail.(NO ITERATIONS).

CASE 2:when I refresh my screen(without clicking inbox link) , I am getting error as

400 That’s an error.

Your client has issued a malformed or illegal request.

That’s all we know.

My question is , Is Gmail is perfectly coded to remove indefinite iterations? or I am getting this error message due to some network overload (like network congestion)? or Someother reasons?

Please explain the mechanism behind this.

Answer 1

Don't know exactly, but my guess is that when trying to do the delivery, the gmail server is looking up and figuring out the chain of forwards right from the start, in order to do the delivery properly the first time (rather than send the message on to itself, where it has to do another lookup, and so on). Given that, it would trivial for them to notice loops and break them.

Remember, though, that even if you get around that first level mechanism (perhaps by boucing out of gmail to another domain and back in), whenever a mailer passes on a message to another mailer (as in the case where you have a filter that forwards the message off to another domain), a 'Received' line is added to the message. I suspect that most mailers will eventually notice if you create a bounce loop involving them, because when the message comes back, the mailer will see that it already dealt with it, and can try to break the loop in various ways.