My client doesn't receive my emails

My client doesn't receive my emails

My client doesn't receive my emails

The domain name of my client is grupomok.com

My domain name is optimice.com.pe in Zoho.
I can receive their emails but they cannot receive my emails.
This issue started on September.
I don't get notifications after to email sent.

My email is:
macevedo@optimice.com.pe
The email of my client is:
cosme.soriano@grupomok.com

Thank you for you support.