What is the best way to scan/prevent your emails from spam filtering?

[Geoff_Krajeski1]

Our team has recently encountered some of our own emails coming through as "SPAM: SUSPECTED: [SUBJECT HERE]" 

We have even taken steps to whitelist the *.mktomail.com domain, but what worries me is that it is just MY network.  Our clients and contacts are likely not adding these whitelist parameters.

What tools are at our disposal, preferrably free, to help proof emails and avoid getting flagged as spam?

Knowing that there are several services out there, is there any service or tool that provides a good view of "all" of these?
McAfee Email Gateway (Ironmail)
Trusted Source
Bayes or Bayesian
etc...
 

[Anonymous]

ReturnPath and SenderScore.org are a couple of the most reputable services out there that I know of, and which offer quite a bit of resources in the way of email optimization and sender reputation management.  Some of it is free and some not, but definitely worth a look IMHO.

[Josh_Hill13]

Agree with Nate as a way to check if your overall reputation is good or not. But Marketo runs email on shared IPs (unless you bought a dedicated one), so if you discover your IPs are negative, speak to marketo deliverability about fixing that.

There are many threads on managing deliverability and looking up bad emails. Start here: http://www.slideshare.net/jdavidhill/marketo-email-reputation-management

What I do is pull a list of people who Hard Bounced and then a list of people who Soft Bounced and I check their Bounced Reason codes. It is easier to export and use excel to filter. I look for denied/spam/blocked emails and then match IPs against sender score. But I also look at the reasons to see if the email is a spam trap.

Automated blockers are setup to manage spam traps, competitors, and multiple bouncers to reduce problems with overal reputation and target servers.