SRV or service record is specifying service at specific Port in domain name system. Protocol like SIP require this to be setup. If you are planning to use office 365 then SRV will have to be setup at your DNS provider.

How to add SRV record using cPanel

You are trying to setup new script and suddenly getting 500 Internal Server Error on all pages. This is generic error message and no details are provided as what is the actual cause of error.

Website 500 Internal Server Error Fix

Do you want to find files from thousand of files in script with specific string, For example which page exactly is showing copyright or from which included file specific function is being called. This can easily be done by using linux find command

Find files with specific string using Linux find command

You have setup SSL certificate and want to show entire site from https even if user access site without https for example if user access http://yourdomain.com it should automatically redirect to https://yourdomain.com If your script do not support internal SSL redirect then this can be easily setup using this rewrite code in site .htaccess file

Force SSL https using .htaccess

Gmail Full Headers
When it comes to spam filters of free email service providers Gmail spam filters are most sane, Gmail will only block your mails or send them to spam folder if there is pattern of spam or broken configuration from your mail server. Gmail will also provide specific error in mail marked as spam providing details as why your mail is marked as spam. Other ISP will not provide you this detail. You have to check "Why is this message in Spam" message gmail display when you open mail from spam folder.

Gmail Sending Mail to Spam Folder