I recently started a thread on Emails and Spam on  the Standing Start Profits  forum. One post to the thread required a reply that I think you may find  valuable here.   
"Something weird happened to me last night. I got  an email from a friend with a picture embedded in the email. My ISP, Charter,  won't allow embedded pictures, so they must be attached. 
When I attached it and sent it to 10 friends, it  got sent back to me with the following message, "the return address  refused the email." Well, I was the return address. Charter had  accepted the email with the picture 10 minutes before I sent it  off.
Since it was a picture of 12 Nuns standing in a  line, holding rifles, and the caption was "The 12 Virgins waiting in Heaven for  the terrorists are not what they expect," I presume there's a filter concerning  rifles or something. I emailed them but no answer."
 
After I had finished laughing at the terrorists  getting their reward in heaven, I addressed the issue which is a lot more  serious than Pat, the Standing Start  Profits member, thought!  
 
ISPs can choose their filtering mechanisms to suit  their market. Charter is geared towards family use and they offer parental  control software. This would suggest they would use a strict set of rules on  spam determination. 
 
The rejection of return address is about to become  a very common problem. I was queried a while back on a clients email being  rejected this way. He was using a google mail account, but his ISP was  btinternet. The receiving mail server was trying to verify with the sending  server belonging to btinternet "do you verify the existence of this mail account  on your server?". (I am loosely translating into english 'cos you really do not  want to read through this the way servers actually talk to each other!)  
 
Of course, the btinternet server could only answer  that "no, I cannot verify existence of sender@gmail.com on this server" and the  mail was rejected with the message "the return address refused the  email". 
 
This is a big move in the way emails are being  handled and, as usual, the end users will be the last to know about it! AOL  introduced this sytem nearly two years ago and were hammered in internet forums  over unrouted mails. Microsoft (read MSN and Hotmail) had a deadline for  introduction in November last year, and Yahoo!, EarthLink and Verizon, and  others will be introducing this filter in the very near future. 
 
It would be nice to be able to say that there is an  easy fix for this but no, when the big ISPs got together to agree a standard  implementation, they actually came away with a more splintered approach than  when they started. 
 
Rules for now: Always send mail through the  SMTP server that owns the account in the reply to box. In other words,  you@btinternet.com if you are using the btinternet mail servers as ISP.  you@yourdomain.com only if you have set the outgoing mail server to be  mail.yourdomain.com. 
 
Many users will end up being bounced back and forth  between ISP and hosting provider over this. Transporting mail has an overhead  cost on a server and to avoid this many hosting providers recommend to their  clients that they set their outgoing mail server to that of their ISP. If you  were told to do this, change it now! 
 
I bet you didn't think your post was very serious,  Pat! :lol: