Hi
Iworx-jenna is very good and I did not realise you may not have knowledge/understanding required sorry
Please do not attempt to SSH or run commands on your server - just use the IW-CP
Your domain is listed rcpthosts file as webmail works, which you posted it did
Your Interworx server is not your DNS provider (you have not chnaged namedservers to point to your Interworx server - this is OK bbut msot change nameservers to point to their server)
Your DNS must be made where your domain name is held - eg the company you pay for domain renewal (namecheap)
You would need to edit the DNS for the domain for record SPF and add a mx to it, so it would then match v=spf1 a mx include:spf.efwd.registrar-servers.com ~all
The MX record change could only be advised as I do not know how you have your IW-CP setup, but guess it is default, so you would need to create an A record for mail.changetoyourdomain.url and set IP to match your A record.
The edit your current MX record and change to mail.changetoyourdomain.url
NOTE - changetoyourdomain.url means change this part to your correct domain name - It is also worth noting that only the mail is added for A record as most DNS already add the domain literal
As webmail worked, I think your authentication is not set in Outlook, so please read this from Liquidweb on how to correctly setup email in Outlook email client
If your emails are been sent to spam, it is not Interworx CP but a most likely a mixture of issues, such as SPF above, email content, IP and domain repution etc… and any new email server been used has to build up reputaion, so it is always marked neutral and scored accordingly
I hope that helps a little
Many thanks
John