>    - The sending IP must have a PTR record (i.e., a reverse DNS of the
>    sending IP) and it should match the IP obtained via the forward DNS
>    resolution of the hostname specified in the PTR record. Otherwise, mail
>    will be marked as spam or possibly rejected.
>

Question: Are all people who are getting kicked off using business gmail
accounts as opposed to personal accounts? Also, do they receive some mail
or no mail before getting booted off?

The first thing that came to mind is that. C4l is configured so Reply-to is
the c4l list and Sender is the actual sender when it seems that from an
email handling point of view, the opposite would be preferable.

However, that doesn't explain why all gmail addresses don't have an issue.
My second thought is that if they receive some mail but have delivery
errors for others, the sender email my be delivered via servers from a
domain other than what their return address would indicate. Again, that
doesn't explain why all gmail users wouldn't get booted off, but my
experience is that there are some annoying differences between google for
business and the personal version.

kyle