David Wees asked a question on Twitter today that I thought would be pretty easy to solve:
@bennettscience I probably read the email though. In fact, I at least look at every email I get in order to quickly catalog it.— David Wees (@davidwees) December 1, 2014
p>Turns out, no so much.
In my searching, I did come across a service which reminds you to follow up with emails which are unreplied to you, but not ones which you need to send the reply.
You can use filters and other little workarounds to get it done, but that usually means having to remember to actually add the filter or mark it unread when you're going through your inbox. That's hard to remember to do in the moment, and can even be impossible (like if you're using the mobile app). Luckily, you can combine search operators in the web view to get pretty good results.
The trick is you have to be using a signature so that every email you send has a unique string in it that we can filter out.
For me, I have a link to my website - ohheybrian.com. It's pretty unique, which makes it a good search term. You can use your name, too, but you want to be careful with that in case the sender used your full name - if that's the case, it'll get filtered out.
To find emails which need replies, you want to use is:read -Re: -your_unique_phrase.
This checks for read emails (in case you forgot to mark it unread), without Re:, and without your_unique_phrase.
Mine reads: is:read -re -ohheybrian.
Emails which are part of a thread still show up, but they're based on the last email of the conversation. So, the thread may contain replies, but you haven't replied to the last one you received, which can still be handy.
You can limit it even further by using in:inbox or some other filter, but that isn't usually necessary.
Unfortunately, this isn't perfect, so you'll still need to do some spot checking. There is no perfect solution as of right now (no is:reply filter or something similar) which you can use, but Google does have a good list of the Gmail search operators that you can play with to build some pretty powerful searches.