CentOS - Aug 2009 - advice needed about "554 Too many recipients"

Hi all,

A client of ours just requested to increase the max_recipients in Exim
to 300, since he keeps getting "554 Too many recipients" error when
sending a marketing email from MS Outlook.

Before you tell me to use Pine / Mutt / etc to send plain-text emails
via mailman, this isn't an option.

I would like to know, what are the implications of increasing the
default 100 to 300? If 300 email recipients were added to the "To:"
field, does it establish 300 connections to the SMTP server, or not?

In the Exim documentation
(http://www.exim.org/exim-html-current/doc/html/spec_html/ch14.html#SECID105)
I found this:

"If this option is set greater than zero, it specifies the maximum
number of original recipients for any message. Additional recipients
that are generated by aliasing or forwarding do not count. SMTP
messages get a 452 response for all recipients over the limit; earlier
recipients are delivered as normal. Non-SMTP messages with too many
recipients are failed, and no deliveries are done.

Note: The RFCs specify that an SMTP server should accept at least 100
RCPT commands in a single message."


But, this doesn't tell me if it will have a performance issue with the
server, or if other mail servers will have problems with our mail
server sending the email to so many recipients in one go.

Can someone give me some pointers on this one?

-- 
Kind Regards
Rudi Ahlers
CEO, SoftDux Hosting
Web: http://www.SoftDux.com
Office: 087 805 9573
Cell: 082 554 7532

On Sun, Aug 16, 2009 at 3:50 PM, Rudi Ahlers<rudiahlers at gmail.com>
wrote:
>
> A client of ours just requested to increase the max_recipients in Exim
> to 300, since he keeps getting "554 Too many recipients" error
when
> sending a marketing email from MS Outlook.
>
> I would like to know, what are the implications of increasing the
> default 100 to 300? If 300 email recipients were added to the
"To:"
> field, does it establish 300 connections to the SMTP server, or not?
Locally between Outlook and Exim, no, this won't establish more than
one connection to the SMTP server.  If Exim is acting as a smart
relay, it'll get one copy of the message with the whole list of
addresses in one transaction.

On the "other side" between Exim and the eventual recipients of this
mail, the likelihood is that Exim will make one or two connections per
destination domain.  If all 200+ recipients are at the same domain
(say, all yahoo.com addresses) then Exim may run into problems, but
it's not very likely.

However, if that list grows very much larger, both you and your client
are going to be a lot happier if the client stops attempting to send
out his own marketing mail with Outlook and instead engages a
reputable email service provider.  Assuming, that is, that he has
appropriately confirmed permission to send email to all those people.