I'm using Outlook 2010 with POP3 format w/ email & web hosting by Earthlink. Some msgs. are rejected immediately with this cryptic rejection msg. from "System Administrator" "550 5.7.1 t6J3YQSn031020 This message does not comply with required standards.". The rejection appears to take place before the msg. even leaves my computer. The problem is very erratic. Some msgs. are rejected, most aren't. Some that are rejected are replies in a thread of msgs. that weren't formerly rejected - so content of the msg. doesn't appear to be a factor. Neither is the size of the msg. Email addresses the msg. is being sent to are correct. I suspected the outgoing port, but Earthlink provides none other than 587. FWIW, I have Trend Micro Max Security installed, but they claim the rejection has nothing to do w/ their software. TIA!