Based on our record, Email List Verify should be more popular than Followup.cc. It has been mentiond 2 times since March 2021. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I'll update this if I find more. For now, this seems to be a partial solution. It's a Gmail add on (except I don't use Gmail) that adds reminders. The options when setting reminders include cancelling it if someone replies, and to remind everyone in the thread. If you combine those two, it seems like — if you use Gmail's web client and have $23/month you're dying to get rid of — a decent way to add the feature. Source: over 1 year ago
If you're not getting the right email addresses from ContactOut and it's bouncing back, you could always run the email addresses through something like emaillistverify.com to make sure they're valid before you try to email them. (you should do that always anyway to protect your email deliverability). Source: almost 2 years ago
Emaillistverify.com is the service I use. Source: almost 2 years ago
FollowUpThen - The simplest way to schedule an email reminder
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Boomerang for Gmail - Boomerang for Gmail is a Firefox / Chrome plugin that lets you take control of when you send and receive email messages.
Email Verifier - Email verifier app lets you verify email.