Email Activation Notification from Different Address & Delayed Welcome Flow Emails: What's Going On?

Hi @Shouu, welcome to the community!

Looking at the screenshots, it seems like the first email is coming from Shopify (when an account is created).  You can find this in your Shopify account under: Shopify Admin → Settings → Notifications → Customer account welcome and modify that message there.

Looks like this:

However, as far as I know, Shopify doesn’t allow merchants to disable this Account Creation notification email so I recommend modifying it in a way that is more of a system message like “Your Account is Activated” and then let Klaviyo sending the proper welcoming message.

The second one seems like the one coming from Klaviyo, and if it’s not being sent I would suggest a few troubleshooting options that I listed here in a previous thread:

And some here too:

So yes, Single Opt-In is the first thing you should do.  If there is a delay, make sure your Flow is a “List Triggered Flow” instead of a “Segment Triggered Flow” as List Triggered Flows tend to be faster due to the fact that it doesn’t require any time to process.

See if those help to figure out why those emails aren’t being sent or give us more context of what’s happening.