Google Compute Engine has all standard outgoing SMTP ports blocked by design. Please vote here to get Google’s SMTP behavior changed:
https://googlecloudplatform.uservoice.com/forums/302595-compute-engine/suggestions/10079937-send-and-receive-email-using-tcp-smtp-imap-ports
Until they open the SMTP ports, there will be no good way to send email from their cloud servers. Sendgrid and the others are too expensive and lack many features that are needed.
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