I am getting a bounceback when trying to send/forward email. It always shows 554 DT : SPM
"554 DT:SPM..." is a receiving server error, indicating that it is the content of the message, not our servers, which is getting blocked. Please review your message, especially the subject line, and re-write anything that may sound like a spam message.
This seems to occur with some regularity, but has never indicated that our servers or IP addresses were getting blocked or were on a blacklist. They do have independent error messages for those cases. We have seen these a bunch with 163.com and netease.