In that case, unless the folks who manage your network are doing a very bad job, the corporate network restricts outgoing mail to approved SMTP servers. Most well-run networks denied outgoing mail from lan clients to external SMTP servers 15 years ago to keep infected computers from being spam-bots.
Do either of these connect?
telnet smtp.mailgun.org 25
telnet smtp.gmail.com 25
Sure. If Discourse can connect to it and it will deliver mail, that’ll work.
It’s possible, but it’s not recommended an a violation of Gmail’s Terms of Service.