A common reason for an email bouncing is a prospect entering it incorrectly on your website’s form or popup.  To see if this is the case, try this:  

Click on your welcome flow, then click on ‘view all analytics’

Next click on recipient activity.

Then, click on other → bounced.

This will give you a list of email addresses that bounced.  A quick glace will tell you if there was a typo, such as emails ending in .co or .coms etc..

If you see email addresses that appear to be incomprehensible or are a company, these are likely bots fishing to get your discount code for discount aggregator sites.  

The best way to prevent this is with a double opt-in.  Otherwise, it’s really up to the quality of the traffic being generated to your site for your welcome flow.

Hey @Femy 

Thank you so much for asking the Klaviyo Community for help!

@Jeff Lusczynski is right on how to check your bounce reasons. There are a number of reason from your customers inbox being full or they have a vacation notice active, or like Jeff said, it could be incomplete or false email addresses. The article I linked goes over what Jeff was sharing in more detail. Also check out these other community post that talk about the same topic!

Hope these help further your journey with Klaviyo!

@Jeff Lusczynski are double opt ins something your implement for your clients? Or do you determine on a case by case basis?

Would love to hear your thoughts!

@GVaughan Yes I encourage clients to use double opt-in.  Here’s why:

• Increases overall open rates and reduces bounces which improves the deliverability of all emails;
• Reduces the frequency in which your subscribers mark an email as SPAM;
• It builds a highly curated and engaged list which also saves on monthly Klaviyo fees; 
• If a subscriber isn’t willing to open the opt-in email in the first place, they aren’t likely going to open any of your other emails.  Natural selection at work.
• I cannot state how important deliverability is.  If you have low open rates because of an unengaged list - more of your brands emails will go to spam or promotions.  This will make all of your email marketing initiatives less effective. 

I’ve had clients make more $ with campaigns to a curated list of 500 vs a list of 20K without double opt in. The flip side here is that with double opt-in, you will grow your list more slowly.  But the goal is quality versus quantity.