Hi Doug, it looks like there may have been a recent DNS change at her domain. Just curious, has the timing on the NDRs been over a period of at least 72 hours? I ask this because of the standard propagation time associated with DNS changes. Here's what I found using nslookup:

C:\>nslookup
Default Server: c52893-f
Address: 192.168.1.2

> set type=all
> mcstyles.com
Server: c52893-f
Address: 192.168.1.2

Non-authoritative answer:
mcstyles.com internet address = 192.220.116.62
mcstyles.com nameserver = ns2.webcom.com
mcstyles.com nameserver = master.webcom.com
mcstyles.com nameserver = ns.webcom.com

mcstyles.com nameserver = ns.webcom.com
mcstyles.com nameserver = ns2.webcom.com
mcstyles.com nameserver = master.webcom.com
master.webcom.com internet address = 192.220.116.43

> server master.webcom.com
Default Server: master.webcom.com
Address: 192.220.116.46

> mcstyles.com
Server: master.webcom.com
Address: 192.220.116.43

mcstyles.com nameserver = ns2.webcom.com
mcstyles.com nameserver = ns.webcom.com
mcstyles.com nameserver = master.webcom.com
mcstyles.com
primary name server = master.webcom.com
responsible mail addr = domainadmin.webcom.com
serial = 60
refresh = 10800 (3 hours)
retry = 600 (10 mins)
expire = 3600000 (41 days 16 hours)
default TTL = 1200 (20 mins)
mcstyles.com MX preference = 0, mail exchanger = smtp.webcom.com
mcstyles.com internet address = 192.220.116.62
mcstyles.com nameserver = ns2.webcom.com
mcstyles.com nameserver = ns.webcom.com
mcstyles.com nameserver = master.webcom.com
ns2.webcom.com internet address = 192.220.116.35
ns.webcom.com internet address = 192.220.116.46
master.webcom.com internet address = 192.220.116.43
smtp.webcom.com internet address = 192.220.116.25
smtp.webcom.com internet address = 192.220.116.61
>

You'll note that her primary nameserver is 'master.mcstyles.com,' which in turn has an MX record pointing to 'smtp.webcom.com.' Your NDR references a mail server named 'mail.mcstyles.com.'

It's possible the DNS admin (Krystine?) made a change within the past 24 hours or so, and your name servers haven't yet caught up with those changes. You can always do a similar nslookup to confirm, using your DNS servers. I'd go ahead and do it from here, but I don't know what they are :)

Anyway, that may be a consideration.

Jeff

p.s. If need be, either you or Kristyne can send an email to the responsible mail address (domainadmin@webcom.com) to see what's going on.