Does not collect/send emails with Outlook (using my own Postfix server)

When connected through secureline, emails are not send by Outlook form my own Postfix server.
In the logs:
Apr 9 12:44:52 ns postfix/smtpd[14451]: timeout after DATA (8067 bytes) from 212-83-188-163.rev.poneytelecom.eu[212.83.188.163]
Apr 9 12:44:52 ns postfix/smtpd[14451]: disconnect from 212-83-188-163.rev.poneytelecom.eu[212.83.188.163]

However, everyting is fine

  • using other email providers
  • using another VPN provider

What shall I do for making Secureline working with my server?
Thanks