i think the problem is straight forward and should be very simple to write a perl program for the same, below is the program. i havent run it to check if it works fine. comments are welcome

1. Assuming table 1 having the address has a structure

address_tbl (mailaddress char(255))

2. Assuming table 2 having the count of domains has a structure

domain_count_tbl (domain char(255), count int)

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@maillist = query("select * from address_tbl")

for(i=0;i<scalar(@maillist;i++)
{
 (name,domain) = split(/@/, myvar[i])
 mylist[domain]++
}

foreach $key (keys %mylist)
{
 @res = query("select 1 from domain_count_tbl where domain=$key")
 if (scalar(@res) == 0 )
 {
  query(insert into domain_count_tbl values("$key",mylist[$key]))
 }
 else
 {
  query(update domain_count_tbl set count=mylist[$key] where domain="$key")
 }
}