The EPiServer Mail service treats any non-fatal errors such as an unreachable mail server, inbox over quota, etc (ie, "soft bounces") just like a normal mail server would, it schedules delivery to be retried with an increasing delay. This process is repeated until there is either success (which counts as successful delivery regardless if retries were necessary) or a timeout is reached, which itself is considered a fatal error ("hard bounce").
So in the case of the full inbox it would only register as a bounce if it is full for an extended period of time, normal transient errors are are not registered as a bounce at all (as it's normally not of interest).
However, one may want to not de-list addresses on the first bounce as there is still some room for error.
Because of how the EPiServer Mail Service retries repeatedly grey listing should not normally prevent delivery, only delay it somewhat. (Just like for any normal mail delivery.)
Hi, Is there a any way to distinguish different types of bounces? From what I know, a full inbox or an out-of-office reply could be concidered as a (soft) bounce, and that shouldn't be treated as a hard bounce (invalid recipent).