· Killfile. If people send me too much junk mail (jokes, chain mail, etc.), they get added to my killfile. It's a simple filter that looks at the "from" field and deletes the message if it's one of the addresses I've added to the filter. Every now and then I'll decide to add someone to my killfile, and I'll just open up the filter and add their address.
· Booleans. The filter works much like Gmail's search function, in that you can add search terms such as AND or OR or NOT. So I can look for addresses that are from a number of people (using OR), or emails that must include all of the words on a list (using AND). Use search operator symbols to make it even easier: "|" for OR, space for AND, "-" for NOT, and parentheses to group different terms in your search string.
· Other search terms. Beyond the common terms above, your filters can use other terms such as "from:", "to:", "has:", "is:", "filename:", and "label:", among others. Using these terms, you can make your filters even more powerful.
· Send reminders to someone. One of the things I wish Google would add to Gmail is the ability to send a delayed email. This would allow me to send reminders to someone at regular times. Instead, I sign up for a reminder email service to send reminders (meant for other people) to my gmail address, and then set up filters to forward the reminders to various people depending on the subject or content of the email. It's not perfect, but it allows me to send reminders to different people on a regular basis.
· Calendar and log. I set up Google Calendar to send me reminders of events. You can set up a label ("events") so that your calendar reminders go straight to the label, star the message, and skip the inbox. Now not only are your events in one place, instead of scattered through your inbox, you can unstar the message when you complete the task or event, and now you also have a log of all the things you've done.
· To-dos. This is a commonly used function, but you can email yourself tasks that you need to do, and then set up a filter that has your email address in both the "to" and "from" boxes, that applies the label "to-do" to the message. This will allow you to view all your to-dos in one filter. Or, if you're a GTD fan, you could set up to-dos for each context (@work, @home, @errands, @phone, etc.), by creating different labels for each, and then setting up filters for different email addresses. Email yourself at yourname+work (you don't need the @gmail.com part), and set up the filter to label that address "@work", and so on for each context.
· Follow up. Even if you're not a GTD fan, having a follow-up label is a must. Simply set up a filter with an email address such as "youname+follow" and put it in the "has the words" filter field, and have this filter label it "@follow" and skip the inbox. Now when you send out an email that needs to be followed up on, put yourname+follow in the "bcc" field, and it'll go into your "@follow" label. Be sure to check this label once a day so you can follow up on your emails.
· Send spam to trash. Instead of having Gmail-filtered spam go into your Spam folder (and have the annoying count of unread spam by the folder's name), set up a filter with "is:spam" in the "has the words" field (just click "OK" on Gmail's warning dialog box when you click next step) and "Delete it" as the action. Now all spam messages will go in your trash.
· Archived bookmarks. If you use del.icio.us and other bookmarking services, you can archive them all in a Gmail label ("bookmarks"). Get the feed urls for each of your bookmarking services, enter them in a forwarding service such as rssfwd.com, and then set up a filter to label them all "bookmarks". Now all your bookmarks are in one place, with Gmail's great search.
· Attachments. If you're like me, you like to go through your old emails and delete a bunch of them at a time. I do common searches during the cleanup process, such as "has:attachment", so that I can look through all my bigger emails and delete them. Make this process quicker by making a label and filter for this search, and for any of your common searches, for that matter.
· Media. If you get a lot of media sent to you, such as music files, videos and photos, set up filters ("filename:wmv | filename:mov" for videos, "filename:mp3″ for music, filename:jpg | filename:gif" for photos, or "filename:pdf | filename:doc" for documents). Now you can quickly find any media.
· Backups. Create a second Gmail account for storage, and create a filter to automatically forward any emails with attachments ("has:attachments") to this second address. Now you can delete your old emails without guilt or worry.
· Newsgroups or feeds. You can set up filters for your newsgroups, so they don't clog up your inbox. Or forward your favorite feeds to your Gmail, and automatically label and archive them for later reading. Now you can not only access them from anywhere, but you can search them too.
· Bloggers. If you run a blog, you can have all your blog's comments and pingbacks automatically archived and labeled ("blog"), so your inbox doesn't get filled up fast. Also have your blog stat reports mailed to you and shunted to this label, so you can get a quick look at your blog's success at a glance.
· Delete old sent emails. There's no reason, in most cases, to keep your really old sent emails. Delete them. Create a filter with "before:2006/06/01 label:sent" with "Delete it" as the action (you'll need to click "OK" to Gmail's warning dialog). Every month or so, update the date of this filter.
· No delete. Some emails you don't want to delete — those precious ones from your kids, for example, or maybe ones from your boss. Set up a label ("nodelete") and a filter that puts the nodelete label on emails from (or to) the addresses you want. Now, some of the above filters, add the string "-nodelete" so that it doesn't show these emails. Now you can delete your old sent emails, or your attachment emails, for example, without worry that your kids' or boss' emails will be trashed along with the rest of the riffraff.
· Flickr. Forward your Flickr account's feed to your Gmail, with a filter to automatically label it, and now your photos are searchable through Gmail. You can also set up filters to send notices that certain tags in your Flickr account has new photos to certain relatives.
· Notes. Email yourself notes on web research, on meetings, on books you're reading, on classes you're taking. Set up a filter to archive and label them (if you send notes to yourname+notes, for example). Now they're searchable and archived and accessible from anywhere.
· Twitter. Use your mobile phone to send text messages or IM messages to Twitter, with a keyword at the beginning of each Twitter message (NOTE, TODO, BLOG, FOLLOW, etc.). Forward your Twitter account's feed to your Gmail, and set up filters for each type of keyword ("note twitter" will be labeled "note" for example). Now you can use your mobile device to send notes, to-dos, follow-up reminders and more to your Gmail through Twitter.
· Wildcard. Use the wildcard character (*) for companies that use multiple types of address from the same domain. One great use I've seen is to use the wildcard character for vendors such as Amazon or eBay to make it easier to track online purchases. Create a label ("online shopping") and a filter with such email addresses as "*@amazon.com|*@ebay.com|*@paypal.com|*@barnesandnoble.com".
