As far as I know, no email client for the iPad supports mass deletion. I do mass deletions of gmail from the web app.
That's my experience, too.
And frankly, I don't get it. The standard email app in 5.0.1 at least now enables a (limited) search/select feature. I just don't understand why adding a delete option to a search result set is such a difficult task. (I assume it must be difficult because its value should be obvious.)
. . . I assume it must be difficult because its value should be obvious.)
One man's obvious is another man's oblivious. Obliviously another case of 'darn that auto-correct'.
Well...
Or, could one just shut the email account down and start is up again later?