There are many ways to communicate to your recipient. 

Since my order on 12-12-19, I have not received my hard copy of the ordered Yellowletters.com,  I have not received my copy of the mailed recipient's list as they said I would receive as well.

If so, that would mean the same recipients are getting pounded with mail over and over again, which is too bad.At least with expireds, if you have MLS you can select listings that are very recently expired, like with a month ago, which would probably mean less competition.

Please try 550-5.1.1 double-checking the recipient's email address for typos or 550-5.1.1 unnecessary spaces.

If they report it to us as spam or if you're sending the same message to multiple recipients your ability to send PM's may get blocked by our automatic filters.

You don't want your recipients straining to see what it says.  

DMM WILL work better when you have a website you can send your mailer recipients to for added credibility.Let e ask you this.Do you have a website?

Also, is there some requirement to allow the message recipient to "opt out"?

I am so proud.  After mailing thousands of direct mail pieces, today was the first irate phone call I received.  The exact quote was:"I'm getting sick and tired of getting letters from you wanting to by my house. It's...

The accepted direct mail standard is that the more times you mail to each recipient the higher the response rate.