You can use third party apps (I use Titanium Backup) to delete apps like the stock Android/Google mailer. I never tried deleting it myself, though. There is no real point in doing so for me. ^^
[Edith says: I should mention that I did uninstall some Google apps, using Titanium Backup, and that I am having some trouble since. Google Search keeps crashing all the time, and I currently can’t re-install it from the backup since I stupidly had overwritten the backup later. Now, I’m stuck with that error message; an update of Google Search from the play store cannot be applied due to a storage problem. Bottom line: Make. Enough. Backups. :facepalm: ]