Assuming you're using gmail via mail app, it doesn't have push function (and never has, iirc) - it retrieves mail either on manual or fetch schedule.
Have you tried re-starting the iPhone? I'm not having any issues so far with apps I've been using, including message, tapatalk, etc.
As to downgrading to 4.1, you need to download a 4.1 firmware from somewhere and also have needed to save SHSH blob prior to upgrading to 4.2.1. Also, even if you manage to downgrade, it can sometimes result in missing info/apps/etc.