Attempting to deliver more than a few hundred e-mails per day via SMTP to our own employees on Google G-Suite tends to cause significant delays due to arbitrary quota limitations on the Google side.
We currently have a single corporate postfix server responsible for outgoing SMTP. This server relays any e-mail from internal services to internal recipients to G-Suite.
I have SFP records configured and the e-mail server is registered within G-Suite as a company e-mail gateway.
Often e-mail delivery to G-Suite is rejected with a 450-4.2.1 response from the Google mail exchangers, causing hours of delay.
Specifically this message:
Jan 10 11:57:03 smtp postfix/smtp: A067338013: host aspmx.l.google.com[126.96.36.199] said: 450-4.2.1 The user you are trying to contact is receiving mail at a rate that 450-4.2.1 prevents additional messages from being delivered. Please resend your 450-4.2.1 message at a later time. If the user is able to receive mail at that 450-4.2.1 time, your message will be delivered. For more information, please 450-4.2.1 visit 450 4.2.1 https://support.google.com/mail/?p=ReceivingRate r22-v6si64987734ljb.4 - gsmtp (in reply to RCPT TO command)
This illustration shows the current flow of e-mail from internal systems:
What options may be available to increase the capacity for e-mail from internal systems to employees?
Might we have overlooked some configuration option in G-Suite? Is there some other way to deliver e-mail to G-Suite from internal sources? Can we add more SMTP relays to increase the quotas?
I have discussed the matter with G-Suite Support, who's only recommendation was to send less e-mail. Go figure :)
Considering we are only sending a couple of dozen e-mails per user per day, I'm guessing we are not the first company to see this issue. Hopefully there is a simple solution!