I did not see the requirement that you wanted a script, so, here's how I would do it...
You can use the '-i' switch to edit the file in-place. See perlrun for reference.
If you do not want to create a backup file...$ perl -ni -e '$match=/::mail(\d+)/;print if!$match||$1>7' data
If you do want to create a backup file with extension '.bak'...perl -ni.bak -e '$match=/::mail(\d+)/;print if!$match||$1>7' data
This assumes that the file containing the data is named 'data'.
Here's the nuts-and-bolts explanation, skip it if you already know how it works.
Basically, this will check every line to see if it matches the regex, in your case you wanted to match something like /::mail(\d+)/ to capture the digits (please put whatever regexp you need in there, this is untested and for example purposes only). The match operator is used for two purposes, (1) letting us know if it matched, and (2) capturing the digits of interest if it does match. Here, I store the boolean value in $match for later usage. The second statement is the conditional print, which will print the current line if it did not match or if the value of the captured digits is greater than 7.
Please change it according to your needs.