"Your server does not support the specified connection encryption type. Try changing the encryption method. Contact your e-mail server administrator or your Internet service provider for further assistance".

Note: Yesterday 21/02/2017 the operation was normal on all computers

I believe that some configuration was done by you that makes it impossible to use in this type system.

Made Configurations

SMTP Configuration settings for Zoho Mail - SSL

Outgoing Server Name: smtp.zoho.com

Port: 465

Security Type: SSL 

Require Authentication: Yes. 

SMTP Configuration settings for Zoho Mail - TLS

Outgoing Server Name: smtp.zoho.com

Port: 587

Security Type: TLS 

Require Authentication: Yes.