You can modify the post-commit email sender script to send an email after some commits (e.g. the revision number is a multiple of 5)
To help write the script, you may use svnlook to fetch previous revision logs.
Here's part of a Python script I wrote to send SMS to developers:
#!/usr/bin/python
# -*- coding: utf-8 -*-
import sys, urllib, os
from subprocess import *
repo = sys.argv[2]
rev = sys.argv[3]
cmdlog = 'svnlook log -r %s %s'%(rev, repo)
cmdauthor = 'svnlook author -r %s %s'%(rev, repo)
log = Popen(cmdlog, stdout=PIPE, shell=True).stdout.read().strip()
author = Popen(cmdauthor, stdout=PIPE, shell=True).stdout.read().strip()
And in the post-commit file
#!/bin/bash
export LANG=en_US.utf8
REPOS="$1"
REV="$2"
./sms.py commit $REPOS $REV
You can refer to this example to fetch log information from svn repository by the command svnlook