Invalid response code received from SMTP server while sending email

[robinhood]

I don't know if this is an issue with CiviSMTP but thought I would start here.  While testing a Civimail draft I get this:

Sorry but we are not able to provide this at the moment.
Failed to send data [SMTP: Invalid response code received from SMTP server while sending email. This is often caused by a misconfiguration in Outbound Email settings. Please verify the settings at Administer CiviCRM >> Global Settings >> Outbound Email (SMTP). (code: 452, response: Cannot send an email! An email has been sent to cdhassell@gmail.com with more information.)]

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I logged in to CiviSMTP and tested the settings, and got a successful report:

Civimail User Check : successfully authenticated.
SMTP Authorization Check : SMTP Authorization Succeeded! This proves that the SMTP server is up and that the SMTP Authorization is working with the SMTP username and SMTP password you have entered.
Email Domain Check : The MX records for data.hbg-cpac.org are correctly configured

Also I went to the Outbound Mail Settings page in my site and tested the settings, and got an email with "SMTP settings are correct."  So I am not sure why it fails in sending CiviMail but succeeds when testing the settings.  Can you help?

[shane]

Hello,

This error occurs when the email you are trying to send is above the 1mb limit. This includes the whole email plus attachments.

Was the email you were trying to send above 1mb threshold?

- CiviSMTP Support

[robinhood]

That was it.  The attachment was large enough at 900kb that together with the rest of the email it was over 1mb in total.  Thanks for your help.