Could not instantiate mail function

I am using Yahoo store domain
Below is the error when I test it.
Test Message Sent
wordpress Test email to CTRI2009@yahoo.com

The result was:

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bool(false)

The full debugging output is shown below:

See FAQ

object(PHPMailer)#456 (69) {
[“Version”]=>
string(5) “5.2.7”
[“Priority”]=>
int(3)
[“CharSet”]=>
string(5) “UTF-8”
[“ContentType”]=>
string(10) “text/plain”
[“Encoding”]=>
string(4) “8bit”
[“ErrorInfo”]=>
string(36) “Could not instantiate mail function.”
[“From”]=>
string(18) “CTRI2009@yahoo.com”
[“FromName”]=>
string(24) “Fast Secure Contact Form”
[“Sender”]=>
NULL
[“ReturnPath”]=>
string(0) “”
[“Subject”]=>
string(32) “Test email to CTRI2009@yahoo.com”
[“Body”]=>
string(80) “This is a test email generated by the Fast Secure Contact Form
WordPress plugin.”
[“AltBody”]=>
string(0) “”
[“Ical”]=>
string(0) “”
[“MIMEBody”:protected]=>
string(81) “This is a test email generated by the Fast Secure Contact Form
WordPress plugin.
“
[“MIMEHeader”:protected]=>
string(450) “Date: Thu, 11 Jun 2015 14:18:56 +0000
Return-Path:
From: Fast Secure Contact Form
Message-ID: <6d187276b997c34d78ec3f6e8e7cdfc4@www.ctri2009.com>
X-Priority: 3
X-Mailer: PHPMailer 5.2.7 (https://github.com/PHPMailer/PHPMailer/)
Reply-To: CTRI2009@yahoo.com
X-Sender: ctri2009@yahoo.com
Return-Path: ctri2009@yahoo.com
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
“
[“mailHeader”:protected]=>
string(65) “To: CTRI2009@yahoo.com
Subject: Test email to CTRI2009@yahoo.com
“
[“WordWrap”]=>
int(0)
[“Mailer”]=>
string(4) “mail”
[“Sendmail”]=>
string(18) “/usr/sbin/sendmail”
[“UseSendmailOptions”]=>
bool(true)
[“PluginDir”]=>
string(0) “”
[“ConfirmReadingTo”]=>
string(0) “”
[“Hostname”]=>
string(0) “”
[“MessageID”]=>
string(0) “”
[“MessageDate”]=>
string(0) “”
[“Host”]=>
string(9) “localhost”
[“Port”]=>
int(25)
[“Helo”]=>
string(0) “”
[“SMTPSecure”]=>
string(0) “”
[“SMTPAuth”]=>
bool(false)
[“Username”]=>
string(0) “”
[“Password”]=>
string(0) “”
[“AuthType”]=>
string(0) “”
[“Realm”]=>
string(0) “”
[“Workstation”]=>
string(0) “”
[“Timeout”]=>
int(10)
[“SMTPDebug”]=>
int(2)
[“Debugoutput”]=>
string(4) “echo”
[“SMTPKeepAlive”]=>
bool(false)
[“SingleTo”]=>
bool(false)
[“SingleToArray”]=>
array(0) {
}
[“do_verp”]=>
bool(false)
[“AllowEmpty”]=>
bool(false)
[“LE”]=>
string(1) “
“
[“DKIM_selector”]=>
string(0) “”
[“DKIM_identity”]=>
string(0) “”
[“DKIM_passphrase”]=>
string(0) “”
[“DKIM_domain”]=>
string(0) “”
[“DKIM_private”]=>
string(0) “”
[“action_function”]=>
string(0) “”
[“XMailer”]=>
string(0) “”
[“smtp”:protected]=>
NULL
[“to”:protected]=>
array(1) {
[0]=>
array(2) {
[0]=>
string(18) “CTRI2009@yahoo.com”
[1]=>
string(0) “”
}
}
[“cc”:protected]=>
array(0) {
}
[“bcc”:protected]=>
array(0) {
}
[“ReplyTo”:protected]=>
array(0) {
}
[“all_recipients”:protected]=>
array(1) {
[“ctri2009@yahoo.com”]=>
bool(true)
}
[“attachment”:protected]=>
array(0) {
}
[“CustomHeader”:protected]=>
array(3) {
[0]=>
array(2) {
[0]=>
string(8) “Reply-To”
[1]=>
string(19) ” CTRI2009@yahoo.com”
}
[1]=>
array(2) {
[0]=>
string(8) “X-Sender”
[1]=>
string(19) ” ctri2009@yahoo.com”
}
[2]=>
array(2) {
[0]=>
string(11) “Return-Path”
[1]=>
string(19) ” ctri2009@yahoo.com”
}
}
[“lastMessageID”:protected]=>
string(51) “<6d187276b997c34d78ec3f6e8e7cdfc4@www.ctri2009.com>”
[“message_type”:protected]=>
string(5) “plain”
[“boundary”:protected]=>
array(3) {
[1]=>
string(35) “b1_6d187276b997c34d78ec3f6e8e7cdfc4”
[2]=>
string(35) “b2_6d187276b997c34d78ec3f6e8e7cdfc4”
[3]=>
string(35) “b3_6d187276b997c34d78ec3f6e8e7cdfc4”
}
[“language”:protected]=>
array(18) {
[“authenticate”]=>
string(35) “SMTP Error: Could not authenticate.”
[“connect_host”]=>
string(43) “SMTP Error: Could not connect to SMTP host.”
[“data_not_accepted”]=>
string(30) “SMTP Error: data not accepted.”
[“empty_message”]=>
string(18) “Message body empty”
[“encoding”]=>
string(18) “Unknown encoding: “
[“execute”]=>
string(19) “Could not execute: “
[“file_access”]=>
string(23) “Could not access file: “
[“file_open”]=>
string(33) “File Error: Could not open file: “
[“from_failed”]=>
string(35) “The following From address failed: “
[“instantiate”]=>
string(36) “Could not instantiate mail function.”
[“invalid_address”]=>
string(15) “Invalid address”
[“mailer_not_supported”]=>
string(25) ” mailer is not supported.”
[“provide_address”]=>
string(54) “You must provide at least one recipient email address.”
[“recipients_failed”]=>
string(45) “SMTP Error: The following recipients failed: “
[“signing”]=>
string(15) “Signing Error: “
[“smtp_connect_failed”]=>
string(22) “SMTP connect() failed.”
[“smtp_error”]=>
string(19) “SMTP server error: “
[“variable_set”]=>
string(30) “Cannot set or reset variable: “
}
[“error_count”:protected]=>
int(1)
[“sign_cert_file”:protected]=>
string(0) “”
[“sign_key_file”:protected]=>
string(0) “”
[“sign_key_pass”:protected]=>
string(0) “”
[“exceptions”:protected]=>
bool(false)
}

The Email debugging output is shown below:

See FAQ

Could not instantiate mail function.

https://wordpress.org/plugins/si-contact-form/