We need help with DNS/DKIM/Email Settings

General information for the business: We provide web development services
Description of requirements/functionality: We are currently sending a number of newsletters and automatic emails from some of our company websites but we are not getting hardly any open reports since we changed server.

Since looking into things further are emails seem to have a bad spam score due to a number of things but some of them being:-

DKIM
Reverse DNS
Signatures

I would like someone to look at how the server is setup and the SMTP details and let us know about any issues. I want to get the emails as verified and the lowest spam score as possible. Note: I have done all the usual things like remove HTML, various phrase etcs. In this job I want to focus on the server aspect/DNS/DKIM etc.

I want to understand it too but don't have the time to learn it, I would rather speak to someone who can tell me and get it configured properly.
Specific technologies required: Server Admin
OS requirements: Linux
Extra notes: