ISP is running CF 4, 5, 1, SP2

Discovered a problem recently whereby every 12th message sent from a list
never arrives, have been using the same code for many years and has not changed
since it was first implemented. The code used to reproduce the problem is:-

<CFQUERY NAME="GettheMail" DATASOURCE=#dsn# USERNAME=#usr# PASSWORD=#pwd#>
select * from tblAutoMail where (fldActivate= Yes) order by fldEmail
</CFQUERY>

<CFSET c=1>

<CFOUTPUT QUERY="GettheMail" group="fldEmail">

<cfmail to="catchall@test.co.uk"
from="Testing <test@test.co.uk>"
subject="#fldemail#">
</cfmail>

#c# #fldemail# <br>

<CFSET c = c + 1>

<CFQUERY NAME="AddEmail" DATASOURCE=#dsn# USERNAME=#usr# PASSWORD=#pwd#>
INSERT INTO tblTrace
(fldCounter, fldEmail)
VALUES ('#c#','#fldEmail#')
</CFQUERY>
</CFOUTPUT>

The output to the browser and records inserted into the trace table match the
number of records in the table so the recordset is correctly processed but
mysteriously every 12th message is not delivered, the live site uses the CFMAIL
tag slightly differently, ie <CFMAIL QUERY="GettheMail" to="#fldemail#", but
causes the same problem, no errors are reported by CF.

Have tested a similar routine using ASP and all the mesages arrived
succesfully, my ISP is a bit slow off the mark so I thought I would ask here.

Thanks