Is Zoho intentionally blocking SMTP access from Gmail?

Is Zoho intentionally blocking SMTP access from Gmail?

I've had no trouble accessing my Zoho account by POP3 from my Gmail account. However, although I've checked the settings carefully to be sure they're correct, and Gmail appears to support these settings, repeated attempts to set up SMTP access to my Zoho account from Gmail leads to the error message: "Couldn't reach server. Please double-check the server and port number."

So, is Zoho intentionally blocking SMTP access from Gmail? If so, may I ask why?