I'm a compulsive emailer. If there's an email sitting in my inbox, it's because that's where I want it - not because I haven't read it. A new email rarely remains unchecked and organized for more than an hour. The complexity of my filters and labels make an Opus 12 look like a child's toy.
The thing that was missing, though, was the ability to schedule emails to be sent. Very often I write emails in the wee late hours and would prefer not to train my clients that I'm available at any hour.
I don't know why it took me so long to look for a solution to this, but my Googling quickly turned up Boomerang. Now instead of marking that email as draft until morning, I just click Send Later, type in "tomorrow 7am" and I'm done. So great.
What's more is that Boomerang solves a problem I didn't realize I had. I regularly send requests or questions of clients that need to be answered before I can complete a task. My typical workflow was to send the email, then immediately make a quick calendar entry to follow up in a day to add an extra nudge.
Boomerang has this option built in. Before sending the email, I set this message to "boomerang" back to me tomorrow morning. When I open Gmail in the morning, that message is sitting in my inbox reminding me that I'm waiting to hear back from that client. Repeat.