I have a client's website e.g."aaa.com" hosted on my VPS with Plesk installed. The client manages the domain and he just set up an A record for aaa.com pointing to my VPS server.
The website works fine. However, if any email sent from the website, it doesn't go out of the VPS server. I mean if an email is sent to email@example.com (for example), it is not delivered to the client's mail server. When I look into firstname.lastname@example.org which has been set up on my VPS, all the emails are just there!! Even if I delete this email on my vps, my client's mail server still doesn't receive any emails from the website.
It sounds like a DNS issues, but the client doesn't use my DNS, he purely hosts the site on my server.
Can anyone please help me out?