dkim - Mails marked as spam in gmail for some accounts

I have a couple of domains running on my VPS with VirtualMin.

I have DKIM enabled, reverse DNS is setup and SPF records are added by Virtualmin.

Now I have a main account (admin) which I can easily use to send emails to gmail accounts with, they don't appear in the spam folder.

When I use an additional user from the same domain they ALWAYS go in to spam folder of Gmail.

I tried a couple of spam checkers and they all come back like this:

Main account:
Summary of Results
SPF check:          pass
DomainKeys check:   neutral
DKIM check:         pass

Sender-ID check:    pass
SpamAssassin check: ham

Another user from the same domain:

SPF check:          pass
DomainKeys check:   neutral
DKIM check:         pass
Sender-ID check:    pass

SpamAssassin check: ham

I cannot check gmails spam score, or why they are marked as spam, but are there things I can do? This happends with every domain on the virtualmin installation.

I also found out that some businesses that I wrote to also didn't get my email, probably filtered, but when I wrote them with the main mail address they received it. Exact same message, same outlook 2013 client.