That requires you to be able to send them a certified letter or have a process server hand-deliver the notice. 

I have mail 50 - 60 letters.

I did keep the EMD from the 2nd buyer -- I had to write a letter and drop it off at the title company because my agent didn't do it and I got a certified letter that they were going to release it back to the buyer if they didn't get written notice from me. 

I’m getting ready to leave at the end of the month and my mail forwarding service gets a letter from the town which I have a feeling is important so I overnight ship it to myself.

I'd send a letter to both the neighbor and the HOA informing them that on X day I will be filing suit naming both of them and we can let a judge decide which of them or if both are liable.

I  had a different issue on a property and they put a letter of explanation I wrote in the file, but again it was a different issue. 

Hi Phil, When I have worked with Section 8 clients, I first contact their case worker & let them know a rent increase is imminent, in some cases the Housing Case worker will also send a letter of adjustment showing the "New Tenant Adjustment Rate" to be paid.

I just received a letter stating that the only option they would offer me is a short-sale and that I was not eligible for a forbearance since I indicated I was interested in selling the home. 

Send a letter to the address and see if it gets returned.

Consider including a Proof Of Funds letter to bolster your bid.