Email Settings

General > Mail Protocol
SMTP - If you prefer to use a SMTP service or server. This is generally more reliable, but can be disabled on many shared servers.

PHP Mail Function - Assumes you have an internal mail server. If you choose this option, all other SMTP configuration options are ignored except Host and Port Number. For the PHP mail function host is generally "localhost" and port is 25, but check with your host. Also note that if this is enabled messages are ONLY sent in plain text format. Finally, some servers restrict outgoing messages to none internal mailboxes. If this fails you should try and use SMTP.
General > Host/IP
SMTP host or IP. When using SMTP it is recommended you use a stable SMTP service, like MXRoute or MailGun for mail delivery. This will make your emails more reliable. Any SMTP account can be used. Once your email details are in place use the test button to send a test message to all your accounts. If you still have issues, enable the mail debug log.

IMPORTANT: If you are using Gmail, DO NOT use your Gmail password. You MUST create an app specific password in your Google account and use that. Also, ONLY use SSL if you have SSL installed. If you don't, you should use TLS. For the Gmail port ONLY use 465 or 587.

Use the 'Send Test Emails' to test that your emails are working ok.
General > Username
SMTP username if authentication is required.
General > Password
SMTP password if authentication is required.
General > Security / Port
SMTP security option and port number. Some services require SSL (such as Google) and others (such as Amazon) TLS.
Headers > From Name
Your preferred "from" name for outgoing emails.
Headers > From Email
Your preferred "from" email address for outgoing emails.
Headers > Reply-To Name
Your preferred "reply-to" name for outgoing emails. Only for emails sent to system admin. In a lot of cases the reply address will default to the person contacting you.
Headers > Reply-To Email
Your preferred "reply-to" email address for outgoing emails. Only for emails sent to system admin. In a lot of cases the reply address will default to the person contacting you.
Options > Additional Notification Email Addresses (CC) (Comma Delimit)
Enter additional emails if you want notifications to go to other addresses besides your main address. Separate with a comma if you are using multiple. Additional emails are sent via Carbon Copy.
Options > SSL/TLS Only - Do Not Verify Certificates
Enable if you are having mail issues with certificates on later versions of PHP. This is not recommended.
Options > Enable SMTP Debugging
Useful if you are having mail issues. If enabled, writes to 'logs' folder. This should be disabled when you are sure everything is working ok.