CDO Mass Email

I have a test and production environment. The code works fine on test
but behaves erractically in production. The script needs to email people
who are subscribed to a particular service. On test it is a small list
but the list on production is fairly large. Does the CDO object have a
maximum number of people that can be BCCed? I also have email addresses
with hyphens in them, are there special characters, (other than @), that
have to be respected? I have seen some other posting with people having
issues with the CDO object and one of the suggestions is to:

# Try using a SendUsing value of 1 (pickup) instead of 2 (port). E.g.
the following line:

cdoConfig.Fields.Item(sch & "sendusing") = 2

Becomes

cdoConfig.Fields.Item(sch & "sendusing") = 1

What is the difference between these two? The webserver is juts using
the default SMTP server, is it going to work with a setting of
cdoConfig.Fields.Item(sch & "sendusing") = 1? Where are they picking it
up from?