laposte.net problems?

[Mjc]

One of my email addresses is with laposte.net.
During the past few weeks, many, but not all, of my sent emails are returned with a message saying that they are unauthorised and therefore refused. In the past week, when trying to download mail, the connection is constantly cut, with no obvious explanation.
Does anyone else have similar problems with laposte?
I have emailed them three times asking for an explanation, and despite an automatically generated reply promising a 24 hour answer, I have received nothing.