Hey Enrico, 

Customer.io automatically filters emails that do not meet the RFC 5322 standard. 

Customer.io doesn’t filter addresses beyond this standard, with the exception of profiles that return a hard bounce. 

You may consider using a dynamic segment to filter addresses that do not return a hard bounce and have an invalid address.

For instance, a segment similar to the following should capture a majority of the failed addresses -

Note: I’ve added an “at least 10 times” condition to this example as you may want to safeguard against profiles that return a failed delivery as a result of malformed liquid in message content, etc…

As Travis is mentioning above the audience can be adjusted with customer segments. I’ve added a filter on the Trigger, not to let anyone further from the very beginning that doesn’t have a correct email. Then the segment itself includes a list of the most common email mis-spellings. This filter out most of the contacts quite ok.

@Enrico Have you seen the Emailable integration? https://help.emailable.com/en-us/article/integrating-with-customerio-3ln0gv/ 

I haven’t used it. Looks like they may help with some automated list cleaning at the delivery level.