Crazy hard bounce when importing eligible contacts from Mailchimp; what could have happened??

[GSoares]

Hello,
Today, I sent my first mass email using Hubspot, with an explosive hard bounce rate of almost *13%* and zero soft bounces.
My sentout was canceled after sending to the first 200 contacts.
 
I am curious to know what happened.
I used the contact list imported from Mailchimp. Of course, this list didn't include Mailchimp's "Cleaned" contacts. I also made sure to add the "Unsubscribed" contacts from Mailchimp as an "opt-out list" in Hubspot, just in case.

Our last email on Mailchimp was sent in late May, with a hard bounce of 2,78%; considering both hard and soft bounces, then the rate was 14,61%.

What could have happened?

After Hubspot stopped the email, I managed to clean my list from all the previously soft-bounced contacts on Mailchimp and scanned my contacts again using a validation service. As a result, I excluded around 20% of our contacts. Then, I sent the email again from Hubspot, and the hard bounce rate was *0.55%*, again with zero soft bounces.
 
But is it possible that around 20% of our contacts became invalid in 3.5 months?? Has it happened to anyone?

Thank you!

[Jnix284 · Accepted solution]

@GSoares yes, it's 100% possible that your contact list degraded by 20% in that amount of time, MailChimp also fails to capture hard bounce as well as HubSpot (IMO), there are a lot that make it through as soft bounce.

[GiantFocal · Accepted solution]

Hi @GSoares,

A 20% decay rate over that period is high but not unheard of, especially if the list hadn't been cleaned recently.

Another reason may be that Hubspot and Mailchimp may categorize and handle bounces differently. What Mailchimp considered a soft bounce may have been treated as a hard bounce by Hubspot.

And note that the first send from a new email service provider can sometimes trigger higher bounce rates as recipient servers adjust to the new sending patterns.

[Jnix284 · Accepted solution]

@GSoares yes, it's 100% possible that your contact list degraded by 20% in that amount of time, MailChimp also fails to capture hard bounce as well as HubSpot (IMO), there are a lot that make it through as soft bounce.