Can not receive mail from my @mydomain.com senders

Can not receive mail from my @mydomain.com senders

Hello, I confirmed ownership and had mx records filled in correctly. I can send mails and receive mails from other sources, i.e yahoo, webmail, etc. but I can not send mails to other users I have created with @mydomain.com extensions. It used to work fine but now I can not use mail forwarding, etc. Any way to fix that?