Undelivered Mail Returned to Sender

[Mail Delivery System]

This is the mail system at host smtp2.pmac.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<collector at domain1.com>: delivery temporarily suspended: Host or domain name
    not found. Name service error for name=domain1.com type=MX: Host not found,
    try again
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