What happens to extra sent mail?

[Marco van Oostende <marco oostende nl>]

Hi,

I recently sent out a mail of several Mb's. During the sending process, which  
took some time, I wrote and sent a second mail. Afterwards, I can't find that  
second mail neither in the Outbox nor in the Sentbox. I got the impression  
that it got sent though, in a separate process. Bug?

Regs, Marco