Some hosts are doing away with backup MX hosts (including me/work) simply because a) any sane sender will retry for a period of at least several hours and b) se

Some hosts are doing away with backup MX hosts (including me/work) simply because a) any sane sender will retry for a period of at least several hours and b) sending via the backup MX is a common way for spammers to (attempt to) increase the chances of their mails getting delivered (e.g., due to lack of/decreased filtering on backup MX hosts).