My client is unable to access your email account

My client is unable to access your email account

Hi!

We have problem. For some reason, my client can´t access his e-mail account.

We receive this message: This account could not be found. Use a different account or sign up for a new account.

But when we try recovery the password, his phone number receive SMS code, and the e-mail (to recovery) works fine.
 
*by Cel Phone App (Zoho Mail) we can send e-mails!

but this message continues.

How can we solve this issue?