We have a customer with a relatively large list of about 311,000 opt-in subscribers. They’ve been collecting opt-ins from their site for years now.

About 240,000 of them are “old” (inactive) subscribers. About 70,000 are relatively “new” (active) subscribers.

They recently segmented their list and sent the same newsletter to each group (separately) over the same IP address, about 6 hrs apart from each other. Around 2pm, they sent the newsletter to the large, inactive list. Around 8pm, they sent the same newsletter to the active list.

The results are eye-opening…

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Word-to-the-wise reports that AOL will begin checking for DKIM Authentication sometime in 2009, as discussed in a recent ESPC call. They’re using DKIM to evaluate your overall “IP reputation” (check out the AOL blog for more on that). MailChimp customers, no need to worry. DKIM Authentication is included by default (and is free) in all MailChimp campaigns (that’s what this box means, in case you were wondering):

Strongmail reports that AOL is filtering email based on your hard bounces. The basic idea is if you’ve got way too many hard bounces, you’ve got bad list hygiene, and they don’t want you sending email to their servers.

If you’re using MailChimp’s managed lists, we automagically clean hard bounces from your list immediately, to prevent this sort of thing. If you manage your list by hand in some excel file, and you manually remove bounces and unsubscribes “whenever you can get to them,” you’re going to have problems (and not just with AOL).  If you’re sending your very first email campaign to an old list you’ve been collecting for years, you should remove any contacts older than 1 year, and then send your campaign in small chunks.

On a related note, here are “average email bounce rates by industry.”

Also, the new MailChimp reports will show you what your bounce rate is by ISP: