To Access iBilling Email Settings Go – Settings -> Email Settings

You can configure outgoing email settings to use built in php mail() function or You can send email through SMTP.

Send Email using PHP built in mail() function:
To send email though php built in mail() function, simply choose this option. Put system email (e.g. you@yourcompany.com).

Send Email using SMTP Server:
Choose SMTP from drop down list. Choosing this a few more option will be appeared.

SMTP Host: Put SMTP host
SMTP Username: Put username for your smtp account
SMTP Password: Put Password
Port: Enter the port number for your smtp provider
SMTP Secure: Choose from TLS or SSL

Use Google’s SMTP Server:
To send email using Google’s SMTP server choose SMTP from the email settings.

Google’s SMTP server requires authentication, so here’s how to set it up:

SMTP server (i.e., outgoing mail): smtp.gmail.com
SMTP username: Your full Gmail or Google Apps email address (e.g. example@gmail.com or example@yourdomain.com)
SMTP password: Your Gmail or Google Apps email password
SMTP port: 587
SMTP TLS/SSL required: TLS
In order to store a copy of outgoing emails in your Gmail or Google Apps Sent folder, log into your Gmail or Google Apps email Settings and:
Click on the Forwarding/IMAP tab and scroll down to the IMAP Access section: IMAP must be enabled in order for emails to be properly copied to your sent folder.

Please note that Google automatically rewrites the From line of any email you send via its SMTP server to the default Send mail as email address in your Gmail or Google Apps email account Settings. You need to be aware of this nuance because it affects the presentation of your email, from the point of view of the recepient, and it may also affect the Reply-To setting of some programs.

In your Google email Settings, go to the Accounts tab/section and make “default” an account other than your Gmail/Google Apps account. This will cause Google’s SMTP server to re-write the From field with whatever address you enabled as the default Send mail as address.

Google limits the amount of mail a user can send, via its portable SMTP server. This limit restricts the number of messages sent per day to 99 emails; and the restriction is automatically removed within 24 hours after the limit was reached.