[Mail delivery failed because of VPN]

I can send e-mails if I exit VPN and it fails sending as soon as I start it again.

[Mail delivery failed because of VPN]

Most of my emails aren’t send anymore. I got this reply:

 

Mail delivery failed: returning message to sender>

>This message was created automatically by mail delivery software.>

>A message that you sent could not be delivered to one or more of its

>recipients. This is a permanent error.>

>The following address failed: ...t-online.de

 

The support of my provider told me, that my IP address (be sent over VPN) are marked as spam because it is on 4 black lists.

>--- The header of the original message is following. ---

...

>X-Spam-Flag: YES

>X-UI-Out-Filterresults:

>junk:10;V03:K0:tzKHYHp5tPs=:vRbCBPM7scTGM3eT1CeAnCuh

 

What should I do?