Title: Invalid mailbox syntax error message
Last modified: May 6, 2020

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# Invalid mailbox syntax error message

 *  [ABCwebsites](https://wordpress.org/support/users/abcwebsites/)
 * (@abcwebsites)
 * [6 years ago](https://wordpress.org/support/topic/invalid-mailbox-syntax-error-message/)
 * I’m getting an error message in all contact forms, saying “Invalid mailbox syntax
   is used”. The error appears in the Additional Headers, even though what I have
   there is exactly as it’s supposed to be (per this page: [https://contactform7.com/adding-cc-bcc-and-other-mail-headers/](https://contactform7.com/adding-cc-bcc-and-other-mail-headers/)).
   This is the setup I have:
    Cc: [info@leadbuilders.nl](https://wordpress.org/support/topic/invalid-mailbox-syntax-error-message/info@leadbuilders.nl?output_format=md)
   Reply-To: [E-mail]
 * Is this a false error or am I doing something wrong? It never used to be a problem
   before.
 * The page I need help with: _[[log in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Finvalid-mailbox-syntax-error-message%2F%3Foutput_format%3Dmd&locale=en_US)
   to see the link]_

Viewing 2 replies - 1 through 2 (of 2 total)

 *  Plugin Author [Takayuki Miyoshi](https://wordpress.org/support/users/takayukister/)
 * (@takayukister)
 * [6 years ago](https://wordpress.org/support/topic/invalid-mailbox-syntax-error-message/#post-12793473)
 * See [Invalid mailbox syntax is used.](https://contactform7.com/configuration-errors/invalid-mailbox-syntax/)
 *  Thread Starter [ABCwebsites](https://wordpress.org/support/users/abcwebsites/)
 * (@abcwebsites)
 * [6 years ago](https://wordpress.org/support/topic/invalid-mailbox-syntax-error-message/#post-12795684)
 * Sorry, but I don’t see what’s wrong with the formats I’m using. How should these
   be formatted for use in the Additional Headers?
 * Cc: [info@leadbuilders.nl](https://wordpress.org/support/topic/invalid-mailbox-syntax-error-message/info@leadbuilders.nl?output_format=md)
   
   Reply-To: [E-mail]

Viewing 2 replies - 1 through 2 (of 2 total)

The topic ‘Invalid mailbox syntax error message’ is closed to new replies.

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 * 2 replies
 * 2 participants
 * Last reply from: [ABCwebsites](https://wordpress.org/support/users/abcwebsites/)
 * Last activity: [6 years ago](https://wordpress.org/support/topic/invalid-mailbox-syntax-error-message/#post-12795684)
 * Status: not resolved