I didn’t find out better title for this article so I named simply “High load, bounces and email marketing” because this article and my last week problem relates to those topics. Last week I was leaving from work when I found that one of our server was under heavy load. I was almost restarting Apache when remembered that I had few days earlier read blog post about how someone had missed why their server was under high load because he had not looked server’s logs.
First thing what I did was start the top and looked what was going on. I found that sendmail was using lot of resources. I knew that there was one campaign which ended previous night and that meant over 50 000 sent emails. In normal conditions sending 50k emails won’t take a long, but this time the problem was poor recipient file. Lot of the emails bounced back to sender.
These bounces was causing the problem because senders email server accepted only few connections from us and after that was rejecting connections from our server with message “too many emails from this server”. Because of that our mail queue was about 15k and most of the queued messages was bounces for our client.
I started wondering why our server was sending bounces to client, because we had set Errors-To header to our company’s bounce address. After some googling I found that Errors-To header isn’t valid header if you look RFC 2076 and after version 2.1 postfix doesn’t use that header anymore.
What we learned from this? Always check out what is really causing the load before you do anything else. We have also have to consider if we could use our own domain as sender because that won’t reject our mails and rise queue unnecessary.
PS. During writing this article I found from Reddit Engine Yard’s blog post “How To Ensure Your Email Gets Delivered” which summon up lot information how to avoid your emails getting rated as spam. I think that article is one must to read for every email sender.
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