It seems that if you have a GMail account synchronized to your Streak, you not only receive email via the "GMail" App. that comes with the device but also in "Email" (@Email that also comes with the device.
So, two lots to delete. I subscribe to YouTube channels, such as "Motors", and periodically it will send a batch of emails advising of new videos which can be played from the emails.
There is another thread that suggests that emails over a certain lengthy size converts to SMS and obviously can't be delivered due to SMS requiring a phone number instead of an email address.
I wonder if that is the case if sending mail via the Gmail app that is supplied on the phone.