If auto-correction is turned on in Outlook, it will capitalize the first character after punctoation or a space. So someone typing tags: will have it changed to Tags:.
Line 1871 of postie-functions.php from Postie 1.3.1 could benefit from a case insensitive search.
Orig line:
if ( preg_match('/tags: ?(.*)\n/', $content, $matches)) {
New line:
if ( preg_match('/tags: ?(.*)\n/i', $content, $matches)) {
This same approach could be used for :start, :end, and others.
Thanks for the plugin.