@trend-1 our mail server was having the same trouble. DO has blocked outbound port 25 (ipv6) wholesale on the network and it doesn't look like they make exceptions. So, the mail server tried to send via ipv6 (haraka prefers ipv6 by default) and wait for sometime to fail. It then tried ipv4 after. For my other VPS, which has IPv6, email was getting blocked in various places anyway because of the "open resolver" issue of IPv6. So, I think 9.0.12 fixes it. Works on both my servers.