Jun 22 11:17:56 mta postfix/smtp: B67511C61EE: host gmail-smtp-in.l.google.com[18.104.22.168] said: 421-4.7.0 This message does not have authentication information or fails to pass 421-4.7.0 authentication checks. To best protect our users from spam, the 421-4.7.0 message has been blocked. Please visit 421-4.7.0 https://support.google.com/mail/answer/81126#authentication for more 421 4.7.0 information. f7si5281662plm.92 - gsmtp (in reply to end of DATA command)
How to solve problem ( recommend of google)
- Sign messages with DKIM
- Publish an SPF record
- Publish a DMARC policy
Ref to check DKIM and spf use dig command
dig -t txt C333XXX-11E4-B123-25B12331CXXXA1._domainkey domain-your.comOr ref to check website online.