If you use any software installed on your computer or laptop, such as outlook, thunderbird, mac mail etc.
You should be aware that when you send the email, the email before it reaches our servers and is sent to the final recipient, it has already recorded the IP that the provider (OTE, Wind, Vodaphone) has given you, these IPs are shared with hundreds of their customers, and because for years they have had port 25 open (open relay) almost all the IPs are on lists stating who is spamming, to get in to remove it ...... they are probably bored ....... so what can you do?

  1. first find the IP you have at your site from here  https://www.whatsmyip.org/
  2. then put the IP here https://mxtoolbox.com/blacklists.aspx and press the blacklist check, if the IP is listed in the results
    1. you can try contacting your provider (let's make a joke) and complain.
    2. you can close your router for five minutes ..... and when you open it again you might have been given another IP (which then again we follow the above steps)
    3. if you fail THERE IS NOTHING ANYONE CAN DO AND THERE ARE ONLY 3 SOLUTIONS
      1. send the email with webmail https://www.todomainmou.gr/webmail (it will not be in the emails in the software used e.g. outlook, thunderbird, mac mail etc.)
      2. switch to business email services such as Outlook exchange or gmail business