These are not message headers in the sense of RFC2822 et al. 'Headers' means the mail summary output: one line per message, containing message number, date, size, sender and first bytes of the subject. That by no means implies "thousands of headers over IMAP" (but it depends on the number of messages in the mailbox, of course).
That being said, having a way to limit the number of lines in the -H output might sometimes be useful. Thanks for the hint. Regards, Sergey
