POP3 provides a special (temporary?) id that stays unique and unchanged at least during the time of the session, even when you delete messages: the uidl. You can use that as the basis for a better tracking system for which messages you've read: with two uidl hashes, you have both the old and the new message number, and by inverting one hash 
%msgnum = reverse %uidl;

[download]
you can map
old message number -> uidl -> new message number
or, in Perl: 
$new_msgnum = $msgnum2{$uidl1{$msgnum}};

[download]

As I currently don't have a pop3 mailbox available for testing purposes, I can't really test it and the code is just pseudocode, just giving a general outline, and not real working code.

But what I don't get... as long as the connection isn't closed, the messages aren't renumbered, or are they? That's how I remember it.

In reply to Re: Help w/ approach using Net::Pop3 by bart
in thread Help w/ approach using Net::Pop3 by GaijinPunch

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.