Problem sending email through Tesconet account

Problem sending email through Tesconet account


Hi, I'm having problem sending email for my Tesconet email account, set up as POP3 in Zoho Mail. Receiving my emails works fine (set up with POP3 server mail.tesco.net, port 110, correct userid and password). When I try to send new email, I get error 421 for mail.tesco.net, port 25. The SMTP is set up with this name and port, no authentication. This appears to be correct setup from the ISP website.
Any idea what the problem can be? I know their SMTP server blocks attempts to send from outside their network.

Thanks for any help - the product seems to work really well apart from this problem