SMTP status code 431 error denotes “Not enough storage or out of memory” problem. So we might think that this error is related to receiving/destination server running out of memory or they don't have enough storage for delivery. However, this error actually relates to the number of recipients the email message has.
To resolve this #error >> https://ibmimedia.com/blog/143/how-to-fix-smtp-status-code-431-error
smtp authentication error
smtp client returned smtp error message
smtp error code 240
#smtp response 221
smtp #email server error
smtp response code 530
smtp 400 error
smtp error 12
