如何为我的域名设置批评

I'm trying to improve email delivery from my domains. I'm using Gmail servers(Gmail MX records).

Recently I've subscribed to critsend. I've successfully used its API to send mails from phpmailer.

Now I need all the outgoing mails from my domain to use critsend services. Critsend documentation specifies this SMTP setup information:

Server: smtp.critsend.com
Port: 25 or 587
Username: [your CritSend username]
Password: [your CritSend password]
Encryption: Plain Text

Where should I add these details? In exim? If I use critsend services will it conflict with Gmail servers?

Thanks in Advance,