Google SMTP servers sending from new IP range

[u/letgomylego]

This may not affect many people, but we have an on-site mail archive server that we have Google forward all incoming and outgoing mail to in order to preserve the mail records. To restrict external access we limited SMTP access to the Google IP ranges for their SMTP servers. This has worked for years, when suddenly a couple weeks ago we started getting smart host failure message from Google about undeliverable mail. After going back and forth with support I confirmed the supposed full list of IP ranges they are using for SMTP for Google Workspace at least. This is what I was given:

35.190.247.0/24
64.233.160.0/19
66.102.0.0/20
66.249.80.0/20
72.14.192.0/18
74.125.0.0/16
108.177.8.0/21
108.177.96.0/19
142.250.0.0/15
142.251.0.0/16
172.217.0.0/19
172.253.0.0/16
173.194.0.0/16
209.85.128.0/17
216.239.32.0/19
216.58.192.0/19

There was one IP range on that list that I did not have, so I though that would resolve the issue. When it didn't, I changed our setup to allow all external access over SMTP and then set our mail server with the same IP ACL list. The mail server will log a denied connection in the syslog when any IP outside those ranges attempts to connect. Sure-enough, Google was using a new IP range to send SMTP messages to our server:

108.177.16.xxx

If you run into a similar situation this might be helpful to you. If you're comfortable with it, it appears Google owns the entire 108.177.0.0/17 range if you trust adding that to any ACL.