Secondary MX

[Samuel Liddicott]

If you have backup MX handled by someone else who doesn't use tarproxy then the secondary MX may be a major source of spam.   Backup MX could be a good way to offload per-domain spam as often backup MX host don't have valid-user information - nearly as good as open relays.  Of course much of the spam may not reach the target, but that is the same as ever, it allows the spammer to quickly spam and depart.   Backup MX should generally be whitelisted by tarproxy or de-listed as MX, there's no point in advertising as backup MX and then applying communications sanctions against it, thus loosing all the mail it aggregated.   I make these points so tarproxy admins can take sensible precautions in either using tarproxy backup MX or whitelisting the backup MX.   Sam