[imp] Problem with mailbox download

[garnier@embratel.com.br]

I´ve checked IMP code for downloading mailboxes as a .mbox file. It passes
the content of all messages in that mailbox to a variable, which is echoed.
Correct if I´m wrong, but I see 2 problems related to that:

1 - there should be a limitation for the mailbox size (I guess it´s
probably related to PHP memory_limit variable)

2 - IMP stays "freezed" while you´re downloading a mailbox. If you click on
any link on the browser (ex: compose new message), the new page isn´t shown
until the download finishes.

Is there any way to avoid these problems?