GMAIL e-mails not being delivered to COMCAST.NET e-mail addresses

We have a Google Apps customer that recently began having issues with email being sent from them to email addresses.  The messages leave their Gmail mailboxes and are received by email servers but then just disappear into the ether.  No delivery, no bounce back.  Everything was working as expected until last week.

I've been researching this for a few hours and have come to the conclusion that this is likely an issue relating to the emails being seen as spam or coming from a spammy server.  So I decided to go to and run a test against the domain.  The negative portion of the results are below...  

Anyone have any thoughts beyond contacting Google and Comcast (which I've already done).  So far the suggestions were: add an SPF record (done), add DKIM.  Any one seen this before and actually resolved it?  I know how to fix the Reverse DNS does not match SMTP Banner when I run the e-mail server, but no idea about how to handle it in GMail... or if it is even the issue.  Comcast certainly isn't being of any real help.

      dns       SOA Serial Number Format is Invalid        More Info
      dns       SOA Expire Value out of recommended range        More Info
      spf       A Valid SPF Record was not found        More Info
      smtp       Warning - Reverse DNS does not match SMTP Banner        More Info
      smtp       5.569 seconds - Warning on Transaction Time        More Info
      smtp       Warning - Reverse DNS does not match SMTP Banner        More Info
      smtp       5.663 seconds - Warning on Transaction Time        More Info
      smtp       Warning - Reverse DNS does not match SMTP Banner        More Info
      smtp       5.710 seconds - Warning on Transaction Time        More Info
      smtp       Warning - Reverse DNS does not match SMTP Banner        More Info
      smtp       5.632 seconds - Warning on Transaction Time        More Info
      smtp       Warning - Reverse DNS does not match SMTP Banner        More Info
      smtp       5.772 seconds - Warning on Transaction Time        More Info
Who is Participating?
Allen FalconCEO & Pragmatic EvangelistCommented:

Comcast has flagged your domain as a source of spam.

First and foremost, you need to scan every system in your domain to ensure you have no malware anywhere.  

Here are 7 steps that have proven successful in getting off blacklists from Google Apps domains:

1) Make sure your domain is really clean and that you are NOT using tiny URLs in your emails (body or footer). Also, make sure you are following ALL of Google's Bulk Senders Guidelines.

2) Make sure your SPF records are clean and correct (make sure you include ANY source of email); If you make SPF corrections, you need to wait 24-48 hours for them to propagate before continuing on. Please note that your SPF should end in "~all", not "-all" or other options. The "~all" suffix appears to make a difference.

3) THEN submit this form to Google. Google does not say how long any action will take. You can try to continue the process after about 24 hours, but you may need to wait 48-72 hours or longer.

4) Test emails to addresses and to addresses running Google Apps for Business/Education
-- the latter should get through first
-- have the recipient mark the message as "Not Spam" if it ends up in the Spam folder

5) If you do not have an account to work with, create one

6) Log into the account, go into settings and Accounts

Setup a "Send mail as" connection to the email address from which you cannot send to gmail addresses (source address)
The source address will receive a confirmation/verification message the link to approve and complete the process
You can now log into your address and send as if you are sending from the source address

7) From you address, send as the source address and send a message to the address

Yes, you are sort of sending a message to yourself
Make sure the message has a subject line and some text in the body
When it arrives back at your account, it will likely end up in:spam.
Find the message and mark it as "Not Spam", this action tells gmail that the sender is not spamming -- and is valid
ParadiseITSAuthor Commented:
As a test, I sent an e-mail from our account through my personal Xeams SPAM filter and it marked it as a 98% probability of being SPAM based on Bayesian... I just don't know exactly why or what to do about it.
spf       A Valid SPF Record was not found

I would start by adding the SPF record to the domain that is using Google Apps.

EDIT:  just reread the question and saw that you added the SPF record, but your results don't seem to reflect that....I would double check the DNS settings for the domain
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ParadiseITSAuthor Commented:
I did do that -- I ran the test before I added the SPF record.
hmmm....I have Google Apps and I get the same reverse dns warning you are getting above.

Have you ran the domain through the blacklist check at mxtoolbox?
ParadiseITSAuthor Commented:
Yes, we have run it through all the tools at MXTookBox -- no blacklists.
Do the emails have a signature?

Only reason I ask is because I had a customer whose ISP randomly started blocking their email due to their signature.
ParadiseITSAuthor Commented:
Yes and no -- we've tried it both ways.  At this point, nothing is getting delivered at Comcast.
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