I am getting this error message when sending emails to several groups in one message using bcc. I do not get this message for all of the contacts in the send list. I am not exceeding the Gmail email limit in a rolling 24 hour period. If I send the exact same message to one of the groups right after I get this message, it goes through just fine. This error started about 3 weeks ago. I have been using this account to send out emails to these groups for approximately 5 years without a problem until this started about 3 weeks ago.
I have tried several ways to alleviate the problem and nothing I can think works.
Technical details of permanent failure:
Message rejected. See https://support.google.com/mail/answer/69585 for more information.