Glad you got it sorted - Team effort

I know nada when it comes to mail servers hence why I pay for a managed service. It was Chrys, who helped me on my forum to rule out some of the basic stuff.

I must admit I too went a bit round in circles at first on my ticket - possibly due to it being weekend and skeleton staff.... sooo... Being a server owner I have access to 24/7 telephone support where they realised it wasn't something simple that needed further investigation. I was promised someone would look at it first thing Monday, which is when Dom spotted the delay and smpt2.lithium dropping the connections. He told me it was something to do with CPanel.

Dom usually knows his stuff and he is one of the reasons why I use Vidahost. (Been with them since the days when it was just Seb & Dom who did everything and before they bought into TSO)

Anyhow, this is bigger than just Vidahost & TSO and others will also be affected.
Plusnet need to get Lithium to ensure their server is configured properly so that other servers dont think they are originators of spam.
Chrys can probably explain it better than me, but Lithium seems to be doing a total of about 4 things incorrectly, which will cause some servers to think they are spewing out spam.