Understanding 'Connection Control' under SMTP Virtual Server properties

This involves Exchange Server 2003 (Enterprise) using an internal IP range of 192.168.100.x.

When building the Exchange server, I wanted to limit connection access to a single IP range outside of the network (a hosted spam filtering service) and to the internal network range.  I went to:  

SMTP Virtual Server Properties > Access > Connection (Connection Control) Connection

I checked "Only the list below" and first entered an IP range that the hosted provider offered.  I wanted to further open access to only our internal range and so I entered " (".  This didn't work as a "blanket range" - instead I had to enter "192.168.100.x (".

The reason is probably very simple, but can someone help me understand why would not work?  I was assuming that it would envelope 192.168.100.x.

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AkhaterCommented: would include the means from to

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james_axtonAuthor Commented:
Akhater, forgive me, but those two statements seem to contradict each other.  I'm sure they don't though - so can you help me understand?
it depends on the subnet mask
A subnet mask of will "include" only the last octet so from to
A subnet mask of will include the last 2 octets so from to

here is an IP subnet calculator http://www.subnet-calculator.com/ it might help
james_axtonAuthor Commented:
Oops, I missed the subnet change the first time I read your post.  Now I see my mistake - I used " (" instead of " (".  The latter would have worked with our range of 192.168.100.x; the former, as I learned, did not work.  Am I reading it correctly now?
" (".  would have worked you are right
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