Stewart85 You are correct.
Most big providers like to see emails signed with DKIM. Unfortunately, you'll have to wait until Enhance releases this feature. It's also a very good idea to get your IP address off the blacklist as well. You'll have to reach out to the blacklist and find their removal form (that's what they usually have somewhere on their website).
One very important thing to note is that there's something called 'email reputation'. It's real, big providers use it in their own way. If you keep this IP address as clean as you can so that it doesn't send spam/nasty emails and/or 'bulk' emails, in a few months you won't have any trouble getting into the larger email mailboxes once DKIM is enabled. If you ever start to have a bad 'email reputation' (which is linked directly to the IP address), the chances of you redeeming the IP reputation are very slim.
In my own personal experience, my clients who need email deliverability use professional email services instead (because those use multiple IPs to send emails), because one wrong move on your IP's side, the reputation is shot and you have clients who start to complain.