website monitoring

This may be a little off topic but here goes. can anyone suggest a secure/reliable website monitoring service? we have number of websites that require monitoring for https,http,smtp etc but would like suggestions from reputable companies.

thx,
gmf

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Securing Apache Web Server with thawte Digital Certificate
In this guide we examine the importance of Apache-SSL and who needs an SSL certificate. We look at how SSL works, how it benefits your company and how your customers can tell if a site is secure. You will find out how to test, purchase, install and use a thawte Digital Certificate on your Apache web server. Throughout, best practices for set-up are highlighted to help you ensure efficient ongoing management of your encryption keys and digital certificates.

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