Sometimes there is no substitute for a snail mail letter. I talked about using Correos de Guatemala and while the letter got there it was about 30 days later. Here is a faster (and cheaper) alternative.

The company is https://mailaletter.com and they will send a letter to anywhere in the world. Their system supports attachments so if you need to send something in a specific format or include a signature, you can do that with an attachment.

Prices start at $1.99. Additional pages are cheap and there are lots of options. I have used them a few times and the letter gets inserted into the local postal system in a day or two.