It looks like SMX may be currently experiencing some issues. Both ourselves and clients sending from Office 365 based email accounts are seeing rejection notices from companies using SMX for spam filtering, when there is no chance the messages are spam (i.e. not marketing emails etc). Speaking to SMX a few minutes ago after logging a case electronically, the rep spoken to was unaware of any issues.
The rejection email message includes:
550 5.7.350 Remote server returned message detected as spam -> 554 5.7.1 We apologise but this message has been rejected due to suspected spam
Their upstream provider CloudMark's web site is currently offline. I hope for their sake it's not a DDOS attack or similar. Chrome tells me:
This page isn’t working
www.cloudmark.com is currently unable to handle this request.
HTTP ERROR 500