Filtering Message based on attachment extension

Question

Hi All,
I have task to develop a java based email client (POP3, IMAP and SMTP based) which only allows email with attachment with certain extension to be downloaded by clients. I develop it with javamail API.
So far my implementation for IMAP is to retrieve all unread/new messages and then check its attachments. All Messages that do not have attachment with intended file extension are discarded and my email client will only present those with intended file extension attachment.
Is there a more efficient way of doing this? can we, for example query the IMAP server by using certain search term so that we only retrieve messages with intended file extension? How about POP3?
Thank you

Answer 1

Very little information is retrieved from the IMAP server to get the
information you need. You can use the search method to reduce
the set of messages you need to consider, and you can use the
fetch method to optimize the fetching of the information needed
to decide whether to display the message. Note that the message
content won't be fetched until you display it.
You can turn on session debugging to see the IMAP protocol
commands being used.
POP3 is completely different. With POP3 you'll need to download
the entire message content to get the information you need to decide
whether to display the message.