Undelivered Mail Returned to Sender

Undelivered Mail Returned to Sender

I am receiving an "Undelivered Mail Returned to Sender" when emailing an estimate to a client. I am able to copy and paste the email body & estimate PDF into my own email client and send that way. It appears to only be an issue when emailing from inside Zoho Invoice.

Here is a copy of the returned message. I've obscured the client's email and domain to avoid spammers:
  1. This is a MIME-encapsulated message


    --q2R3tFjv013175.1332820515/resolver2.sv4.zoho.com


    The original message was received at Mon, 26 Mar 2012 20:55:13 -0700

    from [172.31.251.172]


      ----- The following addresses had permanent fatal errors -----

    <XXXX@XXXXX.com>

       (reason: 550-sv4-smtp2.zoho.com (resolver2.sv4.zoho.com) [72.5.230.67]:37560 is)


      ----- Transcript of session follows -----

    ... while talking to XXXXX.com.:

    DATA

    <<< 550-sv4-smtp2.zoho.com (resolver2.sv4.zoho.com) [72.5.230.67]:37560 is

    <<< 550-currently not permitted to relay through this server. Perhaps you have not

    <<< 550-logged into the pop/imap server in the last 30 minutes or do not have SMTP

    <<< 550 Authentication turned on in your email client.

    550 5.1.1 <xxxx@xxxxx.com>... User unknown

    <<< 503-All RCPT commands were rejected with this error:

    <<< 503-sv4-smtp2.zoho.com (resolver2.sv4.zoho.com) [72.5.230.67]:37560 is

    <<< 503-currently not permitted to relay through this server. Perhaps you have not

    <<< 503-logged into the pop/imap server in the last 30 minutes or do not have SMTP

    <<< 503-Authentication turned on in your email client.

    <<< 503 Valid RCPT command must precede DATA


    --q2R3tFjv013175.1332820515/resolver2.sv4.zoho.com

    Content-Type: message/delivery-status


    Reporting-MTA: dns; resolver2.sv4.zoho.com

    Received-From-MTA: DNS; [172.31.251.172]

    Arrival-Date: Mon, 26 Mar 2012 20:55:13 -0700


    Final-Recipient: RFC822; xxxx@xxxxx.com

    Action: failed

    Status: 5.1.1

    Remote-MTA: DNS; xxxxxx.com

    Diagnostic-Code: SMTP; 550-sv4-smtp2.zoho.com (resolver2.sv4.zoho.com) [72.5.230.67]:37560 is

    Last-Attempt-Date: Mon, 26 Mar 2012 20:55:15 -0700


    --q2R3tFjv013175.1332820515/resolver2.sv4.zoho.com

    Content-Type: message/rfc822


    Return-Path: <zohoinvoicemailbounces+zcf=amanda=functionmarketing.com@zoho.com>

    Received: from [172.31.251.172] ([172.31.251.172])

    by resolver2.sv4.zoho.com (8.13.8/8.13.1) with ESMTP id q2R3tDjv013172;

    Mon, 26 Mar 2012 20:55:13 -0700

    Message-ID: <698429659.1332820513176.JavaMail.sas@invoice.zoho.com>

    Date: Mon, 26 Mar 2012 20:55:13 -0700 (PDT)

    From: Amanda Berlin <amanda@xxxxxx.com>

    To: christy@xxxxx.com

    Subject: Estimate from Function Marketing (Estimate #: EST-256)

    Cc: amanda@xxxxx.com

    Mime-Version: 1.0

    Content-Type: multipart/mixed; 

    boundary="----=_Part_5829_347684101.1332820513166"

    X-Mailer: Zoho Invoice Mailer


    ------=_Part_5829_347684101.1332820513166

    Content-Type: text/html; charset="UTF-8"

    Content-Transfer-Encoding: quoted-printable