Re: [exim] SMTP sessions for multiple recipients when using …

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Author: Philip Hazel
Date:  
To: Joerg Weber
CC: exim-users
Subject: Re: [exim] SMTP sessions for multiple recipients when using a smarthost
On Tue, 25 Jan 2005, Joerg Weber wrote:

> My sendmail guru insists that when using sendmail with a smarthost,
> sendmail will recognize that in the case of one mail with two ore more
> recipients, two or more identical mails are about to be delivered to the
> smarthost and sendmail therefore transfers the mail just once, with
> multiple recipients. That saves bandwidth.


Exim does this by default. For any host.

> What exim seems to do is transfer one mail per recipient, meaning that a
> 2MB mail to 10 recipients generates 2x10MB traffic (instead of just
> 1x2MB).


Only if the default configuration has been changed.

> I'm pretty sure I miss a config option, somewhere. Does max_rcpt and
> serialize_hosts do the trick here?


max_rcpt. Note that its default value is 100.

BUT NOTE: Exim can only send multiple recipients for a single copy if
the copy is identical for all recipients. If your configuration does
things like changing the return path or the headers on a per-recipient
basis, then each recipient is going to need a separate copy.


-- 
Philip Hazel            University of Cambridge Computing Service,
ph10@???      Cambridge, England. Phone: +44 1223 334714.
Get the Exim 4 book:    http://www.uit.co.uk/exim-book