Used Zammad installation type: Kubernetes using Helm
Operating system: Linux
Browser + version: Chrome+ MicrosoftEdge
Using the relay email server. Password reset is ok, creating a ticket ok, email was sent to support team when a ticket opened, as well as when users reply to the ticket.
Expected behavior:
When an admin adds a note into the ticket, the email will be triggered using the Email trigger setting, and email will be sent to customer to alert him/her to check the ticket response from support team.
Actual behavior:
Receive the email but with the error :
Ticket (This is test ticket from support team) has been updated by “-”.
Information:
Unable to send email to ‘user1@abc.com’: undefined method `to_classname’ for nil:NilClass
Steps to reproduce the behavior:
Put a note to the ticket.
Got the error message, coming via email.
Please kindly help, I am new to Zammad and it took me weeks to debug around this but could not find the solution.
Many thanks.
Kind regards,
Nhy
In addition, I found that the default auto reply (on new tickets) also triggered sending email but not successfully, with the same error [Unable to send email to ‘user1@abc.com’: undefined method `to_classname’ for nil:NilClass]
Thanks.
Try removing the sender of the last article from the trigger, since emails are sent by the email account that is configured in the group. This means that the email sends an email to itself.
Thank you @Bozo0511 for your prompt advice. I removed the last article from the trigger and still got the same error.
This is the email Article I got from the rail console. It confirmed that the email was triggered, but could not be sent because of the error [undefined method `to_classname’ for nil:NilClass] in the Preference.
Thank you again for your help.
[3] pry(main)> Ticket::Article.find(116)
=> #<Ticket::Article:0x00007ff0f26dbce0
id: 116,
ticket_id: 29,
type_id: 1,
sender_id: 3,
detected_language: nil,
from: "ZammadHelpdesk <admin@abc.com>",
to: "user@abc.com",
cc: nil,
subject: "New internal note added to Ticket",
reply_to: nil,
message_id: "<20260224102937.29.1308a0fe-62da-4443-9adc-c4a0e7e...",
message_id_md5: "d8bd1407f25602eaf21d99358fc43ce4",
in_reply_to: nil,
content_type: "text/html",
body: "<div>A new note was added.</div><div><br></div><di...",
internal: false,
preferences:
{"perform_origin"=>"trigger", "email_address_id"=>3, "delivery_retry"=>4, "delivery_channel_id"=>5, "delivery_status"=>"fail", "delivery_status_message"=>"undefined method `to_classname' for nil:NilClass", "delivery_status_date"=>Tue, 24 Feb 2026 10:32:16.187320763 UTC +00:00},
updated_by_id: 1,
created_by_id: 1,
origin_by_id: nil,
created_at: "2026-02-24 10:29:37.898000000 +0000",
updated_at: "2026-02-24 10:32:16.189000000 +0000">
