Exchange-couple hundred recipients,mass mailing

I have a client who often sends (exchange) external  e-mail to couple hundred recepients in single mail
and there is a problem because some recipients sends  error "dsn=4.0.0, stat=Deferred: Connection refused by  remotehost."

I presume that is because of mass mailing?
What is the best practices for sending this kind of mails(couple hundred recepients)?
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timgreen7077Exchange EngineerCommented:
Its possible that some of the recipients domains or the recipients themselves don't exist so its being rejected. A few hundred emails its a big deal, the only fear would be it can be perceived as spam and the Exchange server can be blacklisted, and depending on some environments, the mail can be rejected as a result of that also. Generally companies would hire 3rd party companies to deal with large volumes of mass emails going out like that.
Jan MishkinIT ManagerCommented:
Is there a recommended limit on the number of emails to send out via a regular email account to avoid spam?
timgreen7077Exchange EngineerCommented:
By default I believe Exchange allows around 5000 recipient emails which includes internal and external.
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I would never use my internal exchange server in order to do mass mailings. You will get blacklisted and have numerous issues after that. Instead in the past I have recommended services like

to my Clients. just a thought.
another option that is recognized for stability and quality is
Todd NelsonSystems EngineerCommented:
With Exchange, the maximum number of recipients in a single message is "unlimited"; and there is no daily limit ...

With Exchange Online, the maximum number of recipients in a single message is 500; with a daily limit of 10,000 recipients ...

Review these articles for email mass mailing best practices...

I concur with the others, that you should use a 3rd party vendor for bulk emails.

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timgreen7077Exchange EngineerCommented:
By default the maximum number of recipients in Exchange is 5000 (on-prem), but can be changed to allow unlimited recipients:

    Maximum number of recipients - This field specifies the maximum number of recipients in a message. The default is 5000. The valid input range is from 0 through 2147483647. If you clear the check box next to Maximum number of recipients, no limit is imposed on the number of recipients in a message. Exchange 2010 treats an unexpanded distribution group as one recipient.
    Hi Andy,

    Assuming your emails are completely legitimate, then sending out a 'couple of hundred' would be highly unlikely to cause any issues.

    I have clients who have been sending out invoices and statements to customers, running into several hundred each month, for many years, and have never had any issues.  We do it ourselves too.

    Do you have a valid reverse DNS (PTR) record set up?  If not, contact your ISP, and ask them to set one up for you, referencing your domain (they will know exactly that this means).  That may solve the problem, and is good practice regardless.

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