Is it possible to send email directly from a Plesk server hosted on Google Cloud?

Question

• Is it possible to send email directly from a Plesk server hosted on Google Cloud?
• It is not possible to send email from a Plesk server on Google Cloud or a private physical server. Incoming mail is received successfully, but outgoing messages are stuck in the queue. Why?
• How to send an email from a Plesk server on Google Cloud?

Answer

By default, Google Compute Engine blocks port 25 and does not allow outbound connections from it under any circumstances.

Due to this, Plesk server can still receive emails on that port, however sending emails from this port is simply not allowed and that is a major roadblock.

The issue this causes is significant, because you cannot simply change the port, since there is no mechanism for other SMTP servers to know you are using a non-standard port, and you cannot send to other servers using any other port.

The ports 587 and 465 are available for outbound SMTP message submission (RFC 6409: Message Submission for Mail), which means you can use an external mail relay (another server) for authenticated SMTP and this server handles delivery to other mail systems on behalf of your Plesk server, because its port 25 will not be closed for outbound connections.

Due to this, to configure sending emails on a Google Cloud server that runs the Plesk control panel, you must use one of the following solutions:

• Use one of Compute Engine’s third-party partners (SendGrid, Mailgun, and Mailjet) to set up and send emails through their servers.
  

  Note: All these services have a free tier for the Google Cloud customers - 12,000 emails/month on SendGrid, 10,000 emails/month on Mailgun, and 6,000 emails/month on Mailjet.

• Use a Google Workspace account to set up a relay service to send emails through it. Follow the instructions for SMTP relay service settings in the Google Workspace documentation.

Additional information

Installing Plesk on Google Cloud

How to configure Postfix to send email from a Google Cloud server using SendGrid?

How to configure MailEnable to send emails on Google Cloud Platform instance?