Thanks for your feedback. I had considered using Email::Simple. That would solve checking against header entities like from, to, subject, etc. But I also wanted to check if the message contains any of the restricted attachments defined in the configuration. So in my quest for the determining structure of email message cheaply, I also looked at the following:
Email::MIME (thinking it to be lighter than MIME::Parser)
MIME::Structure (the name suggests the ideal solution)
But both of these modules do not drill down into message/rfc822 headers i.e. if I write an email with a covering note and an image attachment, these modules will show that my email contains - text/plain and image/gif, which is what I want.
But if I forward this mail to someone with a covering note then they should show - text/plain, message/rfc822 and its children - text/plain and image/gif from the original msg.
But they show - text/plain and message/rfc822 - they don't drill down into message/rfc822.
And yes, I did call the sub parsing the message recursively for message/rfc822. But then I dumped the object hash of these modules and saw that they stop drilling once they hit the message/rfc822 header. I don't know if it is a design decision but it doesn't help me.
So I am going to do the following - for checking against headers use Email::Simple which benchmarks (using Benchmark module) to be much faster than the same check using MIME::Parser. And for checking attachment names and their mime types, I have no choice but to resort to MIME::Parser.