errorType property

The type of delivery error. Possible string values are:

• "DELIVERY_ERROR_TYPE_UNSPECIFIED" : The default value which should never be used explicitly.
• "RATE_LIMIT_EXCEEDED" : The Domain or IP is sending traffic at a suspiciously high rate, due to which temporary rate limits have been imposed. The limit will be lifted when Gmail is confident enough of the nature of the traffic.
• "SUSPECTED_SPAM" : The traffic is suspected to be spam, by Gmail, for various reasons.
• "CONTENT_SPAMMY" : The traffic is suspected to be spammy, specific to the content.
• "BAD_ATTACHMENT" : Traffic contains attachments not supported by Gmail.
• "BAD_DMARC_POLICY" : The sender domain has set up a DMARC rejection policy.
• "LOW_IP_REPUTATION" : The IP reputation of the sending IP is very low.
• "LOW_DOMAIN_REPUTATION" : The Domain reputation of the sending domain is very low.
• "IP_IN_RBL" : The IP is listed in one or more public [Real-time Blackhole Lists](http://en.wikipedia.org/wiki/DNSBL). Work with the RBL to get your IP delisted.
• "DOMAIN_IN_RBL" : The Domain is listed in one or more public [Real-time Blackhole Lists](http://en.wikipedia.org/wiki/DNSBL). Work with the RBL to get your domain delisted.
• "BAD_PTR_RECORD" : The sending IP is missing a PTR record.