Some of the main issues that are noted in the last infrastructure migration. (September 2014)
1. PHP Warnings – You might experience some PHP warnings regarding deprecated functions that you are using in your site codes.
2. 500 Internal Server Errors – You might experience 500 internal server errors due to incompatible rules enabled in your .htaccess files. Some of the common causes for this error is explained in the link
3. Frontpage Upload Error – You may not be able to update/publish your site using Frontpage extensions in the new infrastructure anymore. It is because Microsoft itself have stopped all the supports for the product Frontpage.
4. Mail Client Not Able to Fetch Mails – You might experience some issues with fetching mails if the configuration is not correct. You need to make sure that the below explained configuration is set in your mail client.
You should use the MX record for your domain as the incoming and outgoing mail server in your mail client. Find out what your MX records are.