When using Groove, it is best to connect your Google mail accounts through oAuth by following this guide:

Getting your email into Groove

However, if you are using a Google Group, you may want to use your SMTP settings to send outbound messages. In Google mail, you must allow "less secure" apps access in order for your SMTP settings to work. There are two places this setting must be enabled:

  1. Visit: https://myaccount.google.com/ and on the left side, go to Security, then scroll down to Less secure app access:
  2. Turn this on, as you must allow it to use SMTP.

At this point, you should be able to successfully connect your SMTP settings to your Groove inbox.