Number five of seven in our occasional series on why ESPs need, or don’t need, lots of IP addresses to send mail properly.
I need multiple IP addresses per customer so as to manage filtering issues
Why this is right
If you have, for example, three dedicated IP addresses per customer and one of those IP addresses gets “randomly” blacklisted, then you can divert traffic to the other two IP addresses temporarily while you resolve the listing.
Why this is wrong
While there are many, many reasons why a source of email can be blocked there are far fewer that affect enough recipients that you really care. If a block affects one guy and one beagle in North Carolina, it’s not worth your operational concentration to care.
Of the blocks you might care about they’re almost all going to be based on recipient response, reputation and content. If one of those blocks affects an IP address you’re sending a mail stream from, it’s probably going to affect the other IP addresses you’re sending the same mail stream from really soon. So the right operational decision is almost always going to be to suspend mailing (either to one particular recipient ISP or to all recipients) until someone has had time to investigate the underlying issue.
Why else this is wrong
If your network engineering decisions are driven primarily by avoiding recipient email filters then you have a deeper business philosophy or customer vetting issue to consider.