It's really just confirming viability, hence the term letter of INTENT. 

If there is no answer leave a hand written letter inside a fed ex envelope. 

This sounds like a balloon ready to explode.

They usually have higher interest costs and a balloon payment. 

Perhaps, your PMC needs a better lease or an addendum to cover issues like this.PMC should send a warning letter that clearly outlines repurcussions of what will happen if the tenant doens't comply.YOU must be prepared for the tenant not paying, requiring eviction and any potential retaliation damage to the property.

In efforts to contact houses that fit our criteria but having issues finding the best service for mailers, post cards, or traditional hand written letters. 

This can be an extremely time-consuming and frustrating process but needs to get done.Borrower Calls – Once the servicer finds your borrower, they’ll make scheduled collection calls notating what transpired and what actions need to be taken.Collection Letters – A variety of collection letters are mailed out based on the delinquency of the borrower.Borrower Statements – Print and mail out monthly borrower statements.Incoming Funds from Borrowers– Any incoming funds from the borrowers will be received, recorded, and distributed to the investor, less the servicer’s fees.Year-End Tax Information – At the end of the year, the servicing company will print out all eligible borrowers who have made interest payments greater than $600.

I know a few people who get calls off letters sure, but its still a vetting process to get to those most motivated. 

I am thinking about sending a carefully worded certified letter as my first attempt to contact them.  

That means the rate will be fixed for 7 years, the payments will be calculated on a 25 year amortization, and there's a balloon payment at the 10 year mark.