Emails sent to customers via C# SMTP go straight to spam for some mail providers

Question

I'm sending emails to customers via our website for communication, and although many providers (Outlook, gmail, yahoo) do not flag the email as spam, I'm finding that Hotmail (Outlook Live) shoves the recieved email directly into Junk Email.

When checking the signature there was quite a few things wrong with the authentication including SPF & the DKIM. These issues have since been fixed, although the emails are still interpreted as spam & I'm unsure how to proceed as my knowledge on the subject is quite limited. The entire signature is quite massive and I can post it upon request, although for now I'll just post the authentication header portion of the email source (The emails were manually X'd out)

Authentication-Results: spf=pass (sender IP is 198.61.254.26)
 smtp.mailfrom=crXXXXXXXXXXX0.com; hotmail.com; dkim=pass (signature was
 verified) header.d=crXXXXXXXXXXX0.com;hotmail.com; dmarc=bestguesspass
 action=none header.from=crXXXXXXXXXXX0.com;
Received-SPF: Pass (protection.outlook.com: domain of crXXXXXXXXXXX0.com
 designates 198.61.254.26 as permitted sender)
 receiver=protection.outlook.com; client-ip=198.61.254.26; helo=
 so254-26.mailgun.net;

Answer 1

It would appear that your sending IP is on a few blacklists. Not all email providers react the same way to blacklisted email addresses, and not all of them check the same lists. You will probably want to use a dedicated email service. This would be my first troubleshooting step.