Email Invalid after hard bounces

[Anonymous]

I know that if the email hard bounces, Marketo marks it as invalid and block further emails. Does anyone know after how many attempts does Marketo mark a particular email as invalid

[Anonymous]

Hi Menaka,
it has more to do with the bounce code than number of attempts:

" Marketo will record an email bounce in all cases, and then based on the bounce code, it may also set email invalid or email suspended.

Email invalid is for permanent errors (for example, "user unknown" or "no such domain"), email suspended is for errors we believe are temporary, such as antispam blocks". 

I Hope this helps

https://community.marketo.com/MarketoArticle?id=kA050000000L3F2CAK
and more about the codes here: https://community.marketo.com/MarketoArticle?id=kA050000000KytYCAS