Trusted
Only just spied this. Disclosure: I worked for SMX several years ago.
If you're getting told your message is suspected spam when you send email to a system protected by SMX, then take it as read - your message is suspected to be spam. This is because at least one of the anti-spam engines they use (they use more than one) has returned a 'spam' verdict when they scanned your email during the SMTP transaction (so before accepting it). The error message goes on to say that you should contact emailsupport@smxemail.com with a copy of the message concerned, or phone them (0800 769 769).
Their stated false positive rate (as of a few years ago) was less than 4 per million SMTP transactions. Yes, FP's will happen. The main engines for detecting spam are signature based (similar to Antivirus) and will be imperfect. Also, people have a tendency to report email they don't want as spam, even if it's something they previously opted-in for (So it was never spam). That 'report as spam' button in many webmail interfaces is just too easy (out of sight, out of mind, and damn the consequences). So if you experience a FP situation it's really important to let them know it's wrong, so they can submit a correction. During their working hours FP's are usually corrected within several minutes.
SMX customers can usually access a web interface that'll show them details of emails that are accepted or rejected (metadata only; spam messages arent' retained or quarantined by default) and provides the means to put in whitelist/blacklist rules to work around system-wide limitations. Whitelisting doesn't fix the root-cause, but it can provide a temporary work-around. I don't know how this works for Xtra's new arrangement, but likely the Xtra Helpdesk could do similar for you.
Final point: SMX have had at least one production incident that affected mail flow through their NZ platform in the last 2 weeks, I can't recall the date (But my employer are an SMX customer and were affected).
Post reflects personal opinions only.
