Title: Gmail API, Assertion failed and Cannot modify header information
Last modified: August 30, 2016

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# Gmail API, Assertion failed and Cannot modify header information

 *  Resolved [Cemtey](https://wordpress.org/support/users/cemtey/)
 * (@cemtey)
 * [10 years, 12 months ago](https://wordpress.org/support/topic/gmail-api-assertion-failed-and-cannot-modify-header-information/)
 * Warning: assert(): Assertion failed in …/www/wp-content/plugins/postman-smtp/
   Postman/Postman-Mail/PostmanZendMailTransportConfigurationFactory.php on line
   63
 * Warning: Cannot modify header information – headers already sent by (output started
   at …/www/wp-content/plugins/postman-smtp/Postman/Postman-Mail/PostmanZendMailTransportConfigurationFactory.
   php:63) in …/www/wp-includes/pluggable.php on line 1196
 * Worked previously, changed provider. Emails are sent out but error shows on screen.
   Using Gmail API.
 * [https://wordpress.org/plugins/postman-smtp/](https://wordpress.org/plugins/postman-smtp/)

Viewing 4 replies - 1 through 4 (of 4 total)

 *  Plugin Author [Jason Hendriks](https://wordpress.org/support/users/jasonhendriks/)
 * (@jasonhendriks)
 * [10 years, 12 months ago](https://wordpress.org/support/topic/gmail-api-assertion-failed-and-cannot-modify-header-information/#post-6231129)
 * Would you please look in Manually Configure > Message
 * Is your email shown in Envelope From Address? This was supposed to be automatically
   set during plugin activation.
 *  Thread Starter [Cemtey](https://wordpress.org/support/users/cemtey/)
 * (@cemtey)
 * [10 years, 12 months ago](https://wordpress.org/support/topic/gmail-api-assertion-failed-and-cannot-modify-header-information/#post-6231130)
 * Fixed by deleting Postman plugin and reinstalling. Under advanced it did not 
   recognize /tmp either at that point when it was broken. Might have been issue
   with extension removal, where I chose to erease files aswell. Therefore perhaps
   it ereased postman files to work as API extension. If so, create update that 
   would cover these files incase others did the same. Error wasn’t visible before
   testing through site.
 * Edit: As answer to question, it was not shown under envelope address at that 
   point. After deletion and installing again it appeared there on it’s own.
 *  Plugin Author [Jason Hendriks](https://wordpress.org/support/users/jasonhendriks/)
 * (@jasonhendriks)
 * [10 years, 12 months ago](https://wordpress.org/support/topic/gmail-api-assertion-failed-and-cannot-modify-header-information/#post-6231132)
 * It sounds like the Activation Handler did not run for some reason :-/
 * No Postman Gmail Extension lives in a separate folder and erasing it wouldn’t
   have caused this.
 * Activate/Deactivate probably would have fixed it as well. Too late to tell now.
 * **Are you on a multisite?
 *  Plugin Author [Jason Hendriks](https://wordpress.org/support/users/jasonhendriks/)
 * (@jasonhendriks)
 * [10 years, 12 months ago](https://wordpress.org/support/topic/gmail-api-assertion-failed-and-cannot-modify-header-information/#post-6231182)
 * I found this just now : From [Function Reference/register activation hook](https://codex.wordpress.org/Function_Reference/register_activation_hook)
 * > _“This hook is now fired only when the user activates the plugin and not when
   > an automatic plugin update occurs”_
 * Well who knew. Postman is five months old and has been doing this wrong since
   the start.
 * This explains so much. :p

Viewing 4 replies - 1 through 4 (of 4 total)

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 * 4 replies
 * 2 participants
 * Last reply from: [Jason Hendriks](https://wordpress.org/support/users/jasonhendriks/)
 * Last activity: [10 years, 12 months ago](https://wordpress.org/support/topic/gmail-api-assertion-failed-and-cannot-modify-header-information/#post-6231182)
 * Status: resolved