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SMTP Proxy - sending email to >50 recipients, split into several SMTP envelopes?

adamgoldberg

I have Exchange 2010 configured to send email to UTM9, which in turn is configured to send email via Amazon AWS SES configured as a smarthost.  Amazon limits the "Maximum number of recipients per message" to 50.  If I want to send an email to 75 people, Exchange connects to UTM and sends something like "MAIL FROM: adam@tld.com", "RCPT TO: [list of 75 addreses]".  UTM dutifully receives the message, and connects to SES and attempts the same transaction (one envelope, 75 recipients), and SES rejects this with  "554 Transaction failed: Recipient count exceeds 50."

I don't see a way to force Exchange to sent at most 50 recipients in one envelope.  There is a "Set-TransportConfig -MaxRecipientEnvelopeLimit", but all that does is cause Exchange to reject the email entirely (the user gets a bounce from Exchange that says "too many recipients").

UTM9 in email->SMTP->Advanced down at the bottom has a "Max rcpt/mail" parameter.  Setting this to 50 doesn't seem to have any effect on /outgoing/ email (at least, not that I could detect).

Exim documentation says:

recipients_max

Type:  integer
Default:  0

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 that the RFCs specify that an SMTP server should accept at least 100 RCPT commands in a single message.

Which would seem to do the same sort of thing that Exchange does -- bounce when the number of recipients is > recipients_max, rather than split it up into several envelopes.

ON THE OTHER HAND, Gnu Mailman uses one envelope per recipient (at least the way I have things configured & using postfix).  This causes everything to work fine, of course.  

 

Is there a way to configure UTM9 to split outgoing envelopes into each <= 50 recipients?  Alternately, to the extent any of you know, is there a way to force Exchange to do this?



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  • 0

    I don't think it's possible even if you were to find and change parameters at the command line - and that might well void your support contract.

    All of my clients use a system separate from Exchange for their mailing lists as you're using Gnu Mailman.  For sending lists of over 50 recipients via Exchange, you can do a mail merge from inside Word using an Excel spreadsheet.

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • 0 in reply to BAlfson

    For mailing lists, yes, Exchange isn't the right solution.  However, outside of mailing lists, it doesn't seem completely outside the range of possibilities to have to send email to >50 individually-addressed people (it's a large group, to be sure, but not outside the range).

    Since I posted this question, I've discovered that sendmail (and only sendmail, not the alternatives like exim (UTM) or postfix (my Mailman installation)) is actually able to split things up like I want (using the r= parameter to a queue).  I may be able to solve my issue by adding a hop, with a VM running sendmail (Exchange -> sendmail-vm (with a queue with r=50) -> UTM -> AWS smarthost.

  • 0 in reply to adamgoldberg

    Interesting, Adam!  Please let us know the result of your attempt.

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • +1 in reply to BAlfson

    Well, I *believe* it worked.  A test seems to indicate that it does work, but I can't figure out how to monitor sendmail's queue handling (debugging sendmail is even more byzantine than configuring it!).  (If anyone reading is a old-school sendmail expert, I'd sure like to hear *how* I can watch sendmail's queue processing)

    I have a bare-bones Centos VM with sendmail installed, configured as a relay with the UTM as its smarthost, with one queue defined with r=50.  I've changed the Exchange send connector from pointing to UTM to pointing to the sendmail VM.  It adds a hop, but not a big deal in my situation.

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