Some organizations have particularly strict policies for their email authentication, and new domains should be whitelisted with the client's IT department. 
Provide the following whitelisting instructions to your client's IT department. 
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SAFELISTING INSTRUCTIONS: 
 
Domain
 
Email Links

There are some companies that need to whitelist by the mail server's IP address. In these cases, we use Sendgrid, with a dedicated IP:

IP 
168.245.105.199