Dear all, I have a very inconvenient problem with my plesk server. While being busy programming a simple PHP Mail() form I discovered that mails send to certain email addresses are not received. For example If I send my email to firstname.lastname@example.org it works perfectly, while sending to email@example.com (and some others) isn't working. I thought that it would be because of Mail() or even Hotmail settings, but there are more email addresses which aren't receiving any emails from any of my domains. -> (so maybe an overall email setting?) And after experimenting with Horde webmail, I found out that emails send from the webmail are also not received by the same email-adresses. NOTE: Strange thing (in my opinion, but maybe this trivial) is that forwarding incoming emails to the non-working email addresses IS working. This really is a huge problem for me and my hosting clients, I hope someone can help me out! Thank you very much in advance!