Why can I not do an SMTP telnet to gmail?

Question

I have tried connecting and using telnet to a gmail service for testing:

telnet gmail-smtp-in.l.google.com 25

Yet it says

Connecting to gmail-smtp-in.l.google.com failed.. Could not open connection to the host, on port 25: Connect Failed

Is this because of my firewall or am I doing something wrong?

I have tested this at work and at home and I am still unable to telnet in.

Yet, when I do an SMTP test using mxtoolbox, it seems that they can telnet in.

Is there something I am missing?

I am trying to do an SMTP test using Telnet.

Answer 1

Your ISP may be blocking outgoing SMTP connections to smtp (25) port as outgoing spam prevention.

Can you telnet smtp (25) port on any email host beyond your ISP network?
Can you telnet smtp.gmail.com 587?
[Port 587 is intended for client to server SMTP sessions, gmail supports it]