Help me tech support!

[silks_ic]

So when I use gmail (with Thunderbird on my computer or on my Blackberry) it sends me a copy of all the mail I send.
E.g.
I get sent an email - this appears in my inbox and on my phone
I reply - this reply appears in my gmail inbox and on my phone (as a received message)

This is rather annoying and I can't find an option to turn it off...