DirectAdmin and WordPress Sending Problem

When I try to send emails through my WordPress contact form or any other plugin, the emails don't seem to be delivered, and I don't receive any error messages. It's causing communication problems with my website visitors, and I need to address this as soon as possible. If anyone has experience with DirectAdmin and WordPress and has encountered similar issues, could you please provide some guidance on how to troubleshoot and resolve this problem? I'm open to any suggestions and steps to diagnose and fix the sending problem.