The first error will occur if the email that is being delivered to the Gossamer Mail user will bring them over their allowed space. So for example, if the user has a 1MB limit, and they are currently using no space (0B), and they receive a 1.1MB email, that email will bounce with that error.

The second error isn't a Gossamer Mail error, but an error from your mail server. Perhaps your ISP is having some connectivity issues?

Adrian