I got into an issue while using a combination of SwiftMailer and Webform on Drupal 9. I found nothing helpfull while Googling and it took me a few days to figure out the issue. Hence I am sharing my findings with you.

My context:

  • Drupal 9.1.3
  • Webform 6.0.2 - with an Email Notification Handler
  • MailSystem 8.x-4.3 - Module: Webform / Formatter: Swift Mailer / Sender: Swift Mailer
  • Swift Mailer 8.x-2.0 - set up to send SMTP emails

The problem:

The website encountered an unexpected error. Please try again later.
TypeError: Argument 1 passed to Swift_AddressEncoder_IdnAddressEncoder::encodeString() must be of the type string, array given, called in /home/www/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/EsmtpTransport.php on line 378 in Swift_AddressEncoder_IdnAddressEncoder->encodeString() (line 32 of vendor/swiftmailer/swiftmailer/lib/classes/Swift/AddressEncoder/IdnAddressEncoder.php).

How the problem manifested:

  • the error above was displayed on the website's footer
  • none of the AJAX driven features of the website didn't work - the ones from the admin interface, nor the ones in the front-end

1 Answer 1


The cause and my solution:

In the Webform's email handler configuration -> "Send from (website/domain)" section -> "From email" field, I used the [site:mail] token.

In EsmtpTransport.php line 378, the $address parameter had a value of ["[email protected]" => string(0)].

By modifying the "From email" field to "Site email address" solved my problem.

Hope this helps.

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