Where do I find a SMTP server to add Custom SMTP when my email client is Zoho?

Where do I find a SMTP server to add Custom SMTP when my email client is Zoho?

I want to add a new "from" address and it prompts me to choose a SMTP server. I wanted to select Zoho's SMTP server since I'm not using any other email client for my domain except this one, but it shows that it may show that it was sent "On Behalf Of" when sent to other emails and I'd like to avoid that. But I'm not sure where to get a custom SMTP server from otherwise. 

Any help would be much appreciated, thanks!