If you are a Mozilla Thunderbird user and were on vacation and you didn't want to/or had a chance to check your email during your break, you'd like to see right away the most important emails you missed once you got back.
I have several Message Filter rules set up that look for specific words in subjects in incoming emails, and also check if the messages are from people in my contact list. Then the rule will set them to Highest Priority and the message is tagged Important. If you have something like that setup, then you can easily, with 2 clicks, check out the emails that are tagged Important that you have not yet read.
On the quick filter bar on Thunderbird you can quickly filter by unread, starred, emails from your contacts, w/ attachments or were tagged. Click on the Tags button
(next to attachment) on the filter bar and you will then see all the important emails. Next, click the "Unread" to the left of "Starred" and there you have it, all the good stuff you need to go through displayed below.
You can also accomplish this another way through the powerful search feature of Thunderbird. Press CTRL-SHIFT-F
to pop up the email finder. Add a rule that says let's say, for instance, "Priority is higher than normal". And click the + button to add another rule of "Date is after START_DATE_OF_YOUR_VACATION". Then add another one that says "Status is New". Click search and you will only see the key unread messages you missed after the first day of your trip. Too bad, however, you can't seem to search through all the mailboxes at once.