Looking at how many external recipients inbound email goes to

March 24, 2013

My data on how many recipients our average inbound email has is in practice incomplete. It's quite possible for a single address here to expand into multiple destinations; some addresses are mailing lists and some people just forward their email to more than one place. So an interesting companion question is how many external recipients a typical email has. To make this more applicable to what I'm interested in, I'm looking at this only for email from the outside world.

As before, this covers 89 days of logs (but because it's a slightly different 89 days, the stats don't necessarily match up exactly). The first number is that out of 1.3 million inbound emails, only 30% had any external recipients at all; the remaining 70% went (directly or indirectly) only to internal recipients. The recipient count breaks down this way:

1 recipient 91.7%
2 recipients 4.6%
3 recipients 1.9%
4 recipients 0.5%
5 recipients 0.4%

As you might expect in an environment with mailing lists, some messages had very high external recipient counts. The champions were emails with between 247 and 266 external recipients, all of which seem to have been messages to department-wide mailing lists (which of course go to a whole lot of people who forward their email to outside addresses). But there weren't very many such emails; only 0.4% of the messages had 10 or more external recipients.

Unlike the inbound email case there don't seem to be any particular pattern for significant numbers of external recipients. This is what I'd expect given that the mapping between the number of inbound recipients and the number of external recipients is a fairly random one (since it depends on exactly who the email goes to).

Written on 24 March 2013.
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Last modified: Sun Mar 24 01:57:21 2013
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