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advice needed about "554 Too many recipients"

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Web Hosting Master
Join Date: Mar 2006
Location: Johannesburg,South Africa
Posts: 598

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 ( 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?

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Join Date: May 2008
Location: Citrus Heights, CA
Posts: 1,671
Marketing Email = Spam?

Is he providing you a valid reason? If not, just say no. Make them go elsewhere to spam.

Best Regards,


Web Hosting Master
Join Date: Dec 2001
Location: Toronto, Ontario, Canada
Posts: 5,792
I'd wager, it's one of those irritating people who CC's a few hundred people in on the funny joke of the week?

Myles Loosley-Millman
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Community Liaison
Join Date: Mar 2003
Posts: 12,199
Moved > Technical & Security Issues.

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WHT Addict
Join Date: Apr 2006
Posts: 113
If 300 email recipients were added to the "To:" field, it won't create 300 connections. It will give just give you those 300 recipients in one SMTP session. The implications of increasing the limit is just that your users can send more email at once.

Increase email deliverability and know who clicked and opened your emails.

SendGrid, reliable SMTP service.

Intangible Asset Appraiser
Join Date: Mar 2009
Location: Austin Tx
Posts: 1,982
Your guy is going to start running into mail server rejecting because of to many addresses. 300 CC is extremely large, and quite a horrible way to do things, not to mention if he doesn't at least use BCC: everyone will see each others addresses.
I would highly recommend requiring him to move to some mailing list software...phplist, etc.

If this is unsolicited email he is sending, also take into consideration he may get your server blacklisted. I demand any large lists have proof of opt-in myself.

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Community Liaison
Join Date: Nov 2006
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I agree with the statements above: ask him to use software or a script that can send in segments rather than all at once.

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WHT Addict
Join Date: Apr 2006
Posts: 113
If he uses some type of software, it will generate 300 emails which will be more inefficient as opposed to one email with 300 RCTP TOs. I agree with changing CC to BCC but besides that, I don't see why it would be better to send 300 separate emails instead of sending one email with 300 RCPT TOs.

Increase email deliverability and know who clicked and opened your emails.

SendGrid, reliable SMTP service.


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