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Outlook error: " Server error: '452 #4.5.3 Too many recipients.' "

Have someone who gets this error message whenever they put more than two email address in the To: field. Even just two addresses causes the error. Only one of the addresses receives the email.

The error message starts with "Your message did not reach some or all of the intended recipients." Then goes on to say..."The following recipient(s) cannot be reached:" and lists them. Finally ends with the error in the Title.

In the past they have used distribution lists a lot. But this error is not the result of using a list, just normal sending.

However the error doesn't occur when an email with two addresses in the To: field is composed from their email provider's webmail site. Neither does it occur if their email account is setup in Outlook on another computer used in another location.

Their internet connection at their house from where they are sending has been checked and is fine.

Anyone got any ideas?


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Last Comment

8/22/2022 - Mon

Open Control Panel, Mail, and delete the Outlook Profile.

Restart the Computer, open Outlook, make a new profile and make a new account.

If Exchange, connect to the Exchange server.
If not Exchange, use the manual account setup to connect to the PST file.

If not Exchange backup the PST file first, although making a new profile should not damage the PST file.
Dr. Klahn

"Server error: '452 #4.5.3 Too many recipients." is generated at the receiving end, so there's little that can be done about it.  The receiving server does not want to see emails targeted to multiple people.  The obvious reason is that they don't want to make it easy for spammers.

However the error doesn't occur when an email with two addresses in the To: field is composed from their email provider's webmail site. Neither does it occur if their email account is setup in Outlook on another computer used in another location.

This cuts down even more finely into the problem.  If there's no trouble when sending from other accounts or systems, then the receiving server specifically does not trust the sender's IP address, email address domain name, or the system name supplied in the HELO/EHLO SMTP negotiation.  All this information is exposed during the initial SMTP negotiation, plus more later on in the DATA segment as it sees message headers, and the server can still reject even though the session is in the DATA segment.  The server does not trust something about the message, but it's not prepared to declare the message unequivocally spam, therefore it is only letting through one email at a time.

As above, there's little that can be done about it.  This error is generated by the receiving server and all that the sender can do is (a) send only one message at a time, or (b) send from a more trustworthy location.

Hi John

Thanks. Did all that but made no difference, Esot
Your help has saved me hundreds of hours of internet surfing.

It seems to me that the message is not legitimate, that is, you can normally send to multiple recipients (I can with Outlook 2016).  I understand what Dr.Klahn has suggested but a limit of 2 is not imposed on any of my recipients. It is still worth checking of course.

Since the new Outlook Profile did not work, try the following:

Make a new, test, Windows User Profile (Account). Log into the new Windows Account. Set up Outlook and test.

Hi Dr Klahn & John,

Apologies for the delay in getting back to you here with an update. Been waiting for feedback and information myself regarding my queries to various people who may be involved, to know more clearly what is going on.

Both are right in a way - first john that's true, that is not normally a legitimate message. And I did all that you suggested but it made no difference. Turns out Dr Klahn is closer to the probable reality of what is occurring.

The person has an ISP for broadband but their email service is hosted with a different provider. The email service provider said their server may be reacting to the fact that many of the IP addresses the email is originating from are in a range that have a "poor" reputation on senderbase.org.  Therefore their server may be reacting to this fact and hobbling outgoing emails from any of those IP numbers to deliver to only one address at a time. They said to get the ISP for broadband to stop assigning so many blacklisted IP addresses (dynamic IP basis).

However the broadband ISP said they aren't assigning blacklisted IP addresses. But we asked for a clean static IP address anyway. At this point they confessed that doing that may not solve the problem. We asked why, and got a mumbled ambiguous response about "there may be a network problem" and they then raised the situation as an issue and gave a case# for it. We suspect there may be other Melbourne customers of theirs complaining about blocked email delivery as well, and that they know it must be their servers or system but don't know what is causing it and/or how to fix it. But at least they are (for now) owning it as their issue and taking responsibility for it.

So for now its a case of waiting to see what develops over next few days. I'll come back here as soon as I have more info on what is at the bottom of this. Thanks for your help so far - always great to have suggestions re the likely best direction to look in.
Dr. Klahn

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Dr Klahn,

Sorry for delay in getting back, with many parties involved the cogs can move quite slowly in these situations.

What you have laid out as the probable cause turned out to be exactly correct - the ISP (not the ESP) have gotten painted with a bad mail reputation, and its affecting many of their customers. I did what you suggested and for now have got the Manager's outgoing mail routing through smtp2go.com (who btw seem excellent, thanks heaps for that tip), which has immediately solved all the problems (they do serve Aussie).

cheers Esot
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