goldenmean

So far, your plugin hasn’t worked either.

That’s what I thought. Thank you for your help.

So, the WP-Mail-SMTP plugin is not compatible with this email service? Because, if I leave the “From Email” in the configuration blank, it will just use the default site wide email address. I tested that and got the same error.

Obviously I could modify the plugin to remove the Return-Path header, but that would be effectively hacking the plugin and breaking future upgrades. Is there some other mechanism by which I could override this behavior?

Okay, here is the output from the test email. Some information has been redacted to protect my information.

Test Message Sent
The result was:
bool(false)
The full debugging output is shown below:
object(PHPMailer)#54 (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(30) "SMTP Error: data not accepted."
  ["From"]=>
  string(29) "XXXXXXXXXXXXX"
  ["FromName"]=>
  string(22) "XXXXXXXXXXXXX"
  ["Sender"]=>
  string(29) "XXXXXXXXXXXXX"
  ["ReturnPath"]=>
  string(0) ""
  ["Subject"]=>
  string(63) "WP Mail SMTP: Test mail to XXXXXXXXXXXXX"
  ["Body"]=>
  string(68) "This is a test email generated by the WP Mail SMTP WordPress plugin."
  ["AltBody"]=>
  string(0) ""
  ["Ical"]=>
  string(0) ""
  ["MIMEBody":protected]=>
  string(69) "This is a test email generated by the WP Mail SMTP WordPress plugin.
"
  ["MIMEHeader":protected]=>
  string(503) "Date: Wed, 10 Jun 2015 17:12:25 +0000
Return-Path:
To: XXXXXXXXXXXXX
From: XXXXXXXXXXXXX
Subject: WP Mail SMTP: Test mail to XXXXXXXXXXXXX
Message-ID: <[email protected]>
X-Priority: 3
X-Mailer: PHPMailer 5.2.7 (https://github.com/PHPMailer/PHPMailer/)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

"
  ["mailHeader":protected]=>
  string(0) ""
  ["WordWrap"]=>
  int(0)
  ["Mailer"]=>
  string(4) "smtp"
  ["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(18) "smtp.office365.com"
  ["Port"]=>
  string(3) "587"
  ["Helo"]=>
  string(0) ""
  ["SMTPSecure"]=>
  string(3) "tls"
  ["SMTPAuth"]=>
  bool(true)
  ["Username"]=>
  string(27) "XXXXXXXXXXXXX"
  ["Password"]=>
  string(13) "XXXXXXXXXXXXX"
  ["AuthType"]=>
  string(0) ""
  ["Realm"]=>
  string(0) ""
  ["Workstation"]=>
  string(0) ""
  ["Timeout"]=>
  int(10)
  ["SMTPDebug"]=>
  bool(true)
  ["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]=>
  object(SMTP)#77 (12) {
    ["Version"]=>
    string(5) "5.2.7"
    ["SMTP_PORT"]=>
    int(25)
    ["CRLF"]=>
    string(2) "
"
    ["do_debug"]=>
    bool(true)
    ["Debugoutput"]=>
    string(4) "echo"
    ["do_verp"]=>
    bool(false)
    ["Timeout"]=>
    int(10)
    ["Timelimit"]=>
    int(30)
    ["smtp_conn":protected]=>
    resource(324) of type (stream)
    ["error":protected]=>
    array(3) {
      ["error"]=>
      string(23) "DATA END command failed"
      ["smtp_code"]=>
      string(3) "550"
      ["detail"]=>
      string(70) "5.7.60 SMTP; Client does not have permissions to send as this sender
"
    }
    ["helo_rply":protected]=>
    string(192) "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
250-BINARYMIME
250 CHUNKING
"
    ["last_reply":protected]=>
    NULL
  }
  ["to":protected]=>
  array(1) {
    [0]=>
    array(2) {
      [0]=>
      string(36) "XXXXXXXXXXXXX"
      [1]=>
      string(0) ""
    }
  }
  ["cc":protected]=>
  array(0) {
  }
  ["bcc":protected]=>
  array(0) {
  }
  ["ReplyTo":protected]=>
  array(0) {
  }
  ["all_recipients":protected]=>
  array(1) {
    ["XXXXXXXXXXXXX"]=>
    bool(true)
  }
  ["attachment":protected]=>
  array(0) {
  }
  ["CustomHeader":protected]=>
  array(0) {
  }
  ["lastMessageID":protected]=>
  string(59) "<[email protected]>"
  ["message_type":protected]=>
  string(5) "plain"
  ["boundary":protected]=>
  array(3) {
    [1]=>
    string(35) "b1_18df0a633bbd73ec1d5b9b45b50eeda1"
    [2]=>
    string(35) "b2_18df0a633bbd73ec1d5b9b45b50eeda1"
    [3]=>
    string(35) "b3_18df0a633bbd73ec1d5b9b45b50eeda1"
  }
  ["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(2)
  ["sign_cert_file":protected]=>
  string(0) ""
  ["sign_key_file":protected]=>
  string(0) ""
  ["sign_key_pass":protected]=>
  string(0) ""
  ["exceptions":protected]=>
  bool(true)
}
The SMTP debugging output is shown below:
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "220 DM2PR07CA0018.outlook.office365.com Microsoft ESMTP MAIL Service ready at Wed, 10 Jun 2015 17:12:25 +0000
"SMTP -> get_lines(): $data is "220 DM2PR07CA0018.outlook.office365.com Microsoft ESMTP MAIL Service ready at Wed, 10 Jun 2015 17:12:25 +0000
"SMTP -> FROM SERVER:220 DM2PR07CA0018.outlook.office365.com Microsoft ESMTP MAIL Service ready at Wed, 10 Jun 2015 17:12:25 +0000
CLIENT -> SMTP: EHLO XXXXXXXXXXXXX.com
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
"SMTP -> get_lines(): $str is "250-SIZE 157286400
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
"SMTP -> get_lines(): $str is "250-PIPELINING
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
"SMTP -> get_lines(): $str is "250-DSN
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
"SMTP -> get_lines(): $str is "250-ENHANCEDSTATUSCODES
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
"SMTP -> get_lines(): $str is "250-STARTTLS
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
"SMTP -> get_lines(): $str is "250-8BITMIME
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
"SMTP -> get_lines(): $str is "250-BINARYMIME
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
250-BINARYMIME
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
250-BINARYMIME
"SMTP -> get_lines(): $str is "250 CHUNKING
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
250-BINARYMIME
250 CHUNKING
"SMTP -> FROM SERVER:250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
250-BINARYMIME
250 CHUNKING
CLIENT -> SMTP: STARTTLS
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "220 2.0.0 SMTP server ready
"SMTP -> get_lines(): $data is "220 2.0.0 SMTP server ready
"SMTP -> FROM SERVER:220 2.0.0 SMTP server ready
CLIENT -> SMTP: EHLO xxx.com
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
"SMTP -> get_lines(): $str is "250-SIZE 157286400
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
"SMTP -> get_lines(): $str is "250-PIPELINING
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
"SMTP -> get_lines(): $str is "250-DSN
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
"SMTP -> get_lines(): $str is "250-ENHANCEDSTATUSCODES
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
"SMTP -> get_lines(): $str is "250-AUTH LOGIN
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
"SMTP -> get_lines(): $str is "250-8BITMIME
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
"SMTP -> get_lines(): $str is "250-BINARYMIME
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
250-BINARYMIME
"SMTP -> get_lines(): $data was "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
250-BINARYMIME
"SMTP -> get_lines(): $str is "250 CHUNKING
"SMTP -> get_lines(): $data is "250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
250-BINARYMIME
250 CHUNKING
"SMTP -> FROM SERVER:250-DM2PR07CA0018.outlook.office365.com Hello [xx.xx.xx.xx]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
250-BINARYMIME
250 CHUNKING
CLIENT -> SMTP: AUTH LOGIN
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "334 VXNlcm5hbWU6
"SMTP -> get_lines(): $data is "334 VXNlcm5hbWU6
"SMTP -> FROM SERVER:334 VXNlcm5hbWU6
CLIENT -> SMTP: bWFpbG1hbkBhZ2VudHB1Ymxpc2hpbmcuY29t
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "334 UGFzc3dvcmQ6
"SMTP -> get_lines(): $data is "334 UGFzc3dvcmQ6
"SMTP -> FROM SERVER:334 UGFzc3dvcmQ6
CLIENT -> SMTP: U3VtbWVyQWdlbnQxNQ==
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "235 2.7.0 Authentication successful target host SN1PR12MB0157.namprd12.prod.outlook.com
"SMTP -> get_lines(): $data is "235 2.7.0 Authentication successful target host SN1PR12MB0157.namprd12.prod.outlook.com
"SMTP -> FROM SERVER:235 2.7.0 Authentication successful target host SN1PR12MB0157.namprd12.prod.outlook.com
CLIENT -> SMTP: MAIL FROM:
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "250 2.1.0 Sender OK
"SMTP -> get_lines(): $data is "250 2.1.0 Sender OK
"SMTP -> FROM SERVER:250 2.1.0 Sender OK
CLIENT -> SMTP: RCPT TO:
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "250 2.1.5 Recipient OK
"SMTP -> get_lines(): $data is "250 2.1.5 Recipient OK
"SMTP -> FROM SERVER:250 2.1.5 Recipient OK
CLIENT -> SMTP: DATA
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "354 Start mail input; end with .
"SMTP -> get_lines(): $data is "354 Start mail input; end with .
"SMTP -> FROM SERVER:354 Start mail input; end with .
CLIENT -> SMTP: Date: Wed, 10 Jun 2015 17:12:25 +0000
CLIENT -> SMTP: Return-Path:
CLIENT -> SMTP: To: XXXXXXXXXXXXX
CLIENT -> SMTP: From: XXXXXXXXXXXXX
CLIENT -> SMTP: Subject: WP Mail SMTP: Test mail to XXXXXXXXXXXXX
CLIENT -> SMTP: Message-ID: <[email protected]>
CLIENT -> SMTP: X-Priority: 3
CLIENT -> SMTP: X-Mailer: PHPMailer 5.2.7 (https://github.com/PHPMailer/PHPMailer/)
CLIENT -> SMTP: MIME-Version: 1.0
CLIENT -> SMTP: Content-Type: text/plain; charset=UTF-8
CLIENT -> SMTP: Content-Transfer-Encoding: 8bit
CLIENT -> SMTP:
CLIENT -> SMTP: This is a test email generated by the WP Mail SMTP WordPress plugin.
CLIENT -> SMTP:
CLIENT -> SMTP: .
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "550 5.7.60 SMTP; Client does not have permissions to send as this sender
"SMTP -> get_lines(): $data is "550 5.7.60 SMTP; Client does not have permissions to send as this sender
"SMTP -> FROM SERVER:550 5.7.60 SMTP; Client does not have permissions to send as this sender
SMTP -> ERROR: DATA END command failed: 550 5.7.60 SMTP; Client does not have permissions to send as this sender

CLIENT -> SMTP: QUIT
SMTP -> get_lines(): $data was ""SMTP -> get_lines(): $str is "221 2.0.0 Service closing transmission channel
"SMTP -> get_lines(): $data is "221 2.0.0 Service closing transmission channel
"SMTP -> FROM SERVER:221 2.0.0 Service closing transmission channel

In case anybody comes looking for this answer. I found a fantastically thorough solution to integrating Contact Form 7 with Bootstrap 3. Just add these lines to your forms.less file or theme.less file and recompile Bootstrap.

input[type="text"].wpcf7-form-control,
input[type="password"].wpcf7-form-control,
input[type="datetime"].wpcf7-form-control,
input[type="datetime-local"].wpcf7-form-control,
input[type="date"].wpcf7-form-control,
input[type="month"].wpcf7-form-control,
input[type="time"].wpcf7-form-control,
input[type="week"].wpcf7-form-control,
input[type="number"].wpcf7-form-control,
input[type="email"].wpcf7-form-control,
input[type="url"].wpcf7-form-control,
input[type="search"].wpcf7-form-control,
input[type="tel"].wpcf7-form-control,
input[type="color"].wpcf7-form-control,
select.wpcf7-form-control
{
    .form-control
}

.wpcf7-checkbox .wpcf7-list-item
{
    .checkbox
}

.wpcf7-checkbox.checkbox-inline .wpcf7-list-item
{
    .checkbox-inline
}

.wpcf7-radio .wpcf7-list-item
{
    .radio
}

.wpcf7-radio.radio-inline .wpcf7-list-item
{
    .radio-inline
}

Then, recompile bootstrap using a command like this:
lessc -x bootstrap.less > path/to/my/folder/bootstrap.min.css
I hope this helps someone.