They block it outbound, not inbound - email receiving should work fine in GCP. I believe that's the only mandatory firewall restriction, and even that one can h

They block it outbound, not inbound - email receiving should work fine in GCP. I believe that's the only mandatory firewall restriction, and even that one can have exceptions made for use cases such as your former employer, as the other reply to you said. The point is to make sure that anything sending email from GCP has someone properly attending to it, so that GCP does not become a source of spam, rather than to prevent email service providers or the like from using GCP. For many companies that aren't an email service provider, it's often a better use of IT funds to send via one anyway, given how much work is involved in maintaining security and deliverability of an outbound email server in 2020. Most of those support sending through ports that aren't 25, and Google has some nice free tier deals for GCP customers.