Dear legitimate email sender or bad actor...
Hello there! Nice to meet you!
You are likely reading this because you attempted to deliver some emails to mail.plaureano.com and failed miserably. Assuming you are not a spammer or a hacker, and that is a big assumption, let's go with it: I have some recommended reading for you: https://snov.io/blog/how-to-avoid-spam-filters/
It's a jungle out there! Unfortunately, email is the most abused Internet service, so you must be careful about what mail you accept on your server and what you discard. However, there are some basic rules I have set on this server that you must follow; otherwise, I will not accept your messages:
Your DNS name must point to your IP. Your reverse DNS must point to your name. Easy pizzi, right?
If you can write to me, I must be able to respond, meaning I will try to call you back (send you an email), and if you are using an open relay or refuse my email, I will not accept any of your messages. I will look up your DNS MX records for the domain you are using to message me and try to message you. It is only fair; after all, you contacted me first.
This should not bother you if you are a legitimate email sender. However, if you are a spammer, it forces you to set up at least an account that receives mail to the address you are using to spam people.
Your DNS must have a valid DMARC, SPF, and/or DKIM. Head to mxtoolbox.com and test your domain name. The report should look similar to the image below.
While you are at it, check your status on blacklists for the domain. You see, people talk to each other, and some friendly folks compile and maintain lists of email servers that distribute spam/malware.
If all of this is too much for you to handle, set up an account with some professionally administered mail provider. Mail administration can be a pain; it is not for everyone.
Have fun, happy emailing, and take care.