MESSAGES - How to pause/stop check new mail?

Question

Background:
I handle mobile email by forwarding my multiple email accounts into a separate POP account to be accessed only by my Playbook.
I only use it once or twice a week when I go out on the road.
My problem is that I receive hundreds of emails daily and they all get dumped into that mobile email account.
Typically, I'll just purge that account using webmail from my PC before I go on the road. That way, my Playbook will only get the messages that come after the purge.
Problem:
That should work, but it doesn't.
Or rather, it ONLY works if I purge that account BEFORE I even power on my Playbook.
If I don't empty the account, the Playbook will automatically check for new messages on the server -- EVEN IN STANDBY MODE.
So, I can't even leave my Playbook on standby between uses without having every single new message automatically received.
Admittedly, it's a nuisance rather than a critical issue.
But it's a hell of nuisance to have to manually delete hundreds of email messages every time I want to use my Playbook.
What I've tried:
Message Sync Interval "Manual" (doesn't work) - setting the sync interval to "manual" doesn't prevent new messages still being automatically downloaded, even in standby mode.
What I want:
Either - "Manual" should truly be manual,
Or - There should be a setting for "off" so that I can choose when I want it to sync.

Answer 1

Go to Settings > Fetch New Data.
Under Fetch, the options are:
Every 15 minutes
Every 30 minutes
Hourly
Manually