Not recieving emails (only from gmail and zoho)

Not recieving emails (only from gmail and zoho)

Hi!

 My client just called me because he didn't get answer to his e-mail... Issue is that I haven't received one yet so I tested sending mails to my zoho mail adress on custom domain from different mail services. Received one from GMail, but mail from Outlook.com and Seznam.cz (biggest mail provider in Czech republic) are still lost...

Any solutions?