I have a dedicated linux server that has 16 IP addresses... and one of those IP address is the main (or shared) IP of the server. So I can host a ton of websites on that one shared IP, and can optionally move individual accounts to one of the 15 other dedicated IP's if I so desire.
I put an account on it's own dedicated IP and it works fine. But I've noticed all my email being sent out is being filtered into people's spam folders... be it hotmail, gmail, yahoo, outlook, etc. My DNS is setup great as far as I can tell (DNSreport confirms) and I have SPF/domainkeys installed for this one account... so I shouldn't have problems authenticating my emails.
The only thing I can think of that would be causing problems for my mail being filtered as spam, is that since this account is on one of my dedicated IP's... that these mail providers (yahoo, etc) are looking at the incoming connection claiming to be the host, which is the main (or shared) IP of the server, and then looking at the MX record for the domain that the email address is, which points to that dedicated IP... and since they don't match... the email provider rejects the email cause the two IP's aren't matching.
Is this a valid assumption? And if so, is there anything I can do about it besides moving that one account back to the shared IP? For the life of me I can't figure this out.