As reported on MyHeritage’s blog, https://blog.myheritage.com/2018/01/contacting-dna-matches-is-now-free/, if you use the DNA match option to send the message.It doesn’t apply to contacting users through other means if you don’t have a paid subscription.
Please note that contacting DNA Matches has been made free, but contacting users through some other contexts (e.g., Smart Matches) still requires a subscription.
This is a great example of a company that listens to its non-paying customers and responds positively.
Also, if you have tested your DNA elsewhere (FTDNA, Ancestry, etc.), you may be able to transfer your results for free to MyHeritage. I believe 23andMe (v5 chip) is the only major company you can’t transfer results from currently and that will probably be resolved shortly. There are over 1 million people who have DNA tested with MyHeritage or transferred their results to MyHeritage (about 20% were transfers and 80% were actually tested). It’s worth the free transfer as some people have only tested with MyHeritage and won’t upload to GEDmatch so the only way you will match those people is by either transferring your results or testing at MyHeritage.