Outlook and Zammad mail header issue


  • Used Zammad version: 5.1
  • Used Zammad installation type: (source, package, docker-compose, …): any
  • Operating system: any
  • Browser + version: any

Expected behavior:

  • Unlimited replies by Customers via Outlook

Actual behavior:

  • Zammad seems to reference all of the previous Mails in the mail headers sent by trigger.
    Header looks like this:

References: <20220323150631.557.e3ec0d3c-53a6-4b42-b658-8e857d2c9622@domain.at> <2f3201d83ec7$aef51160$0cdf3420$@.................

  • We have a trigger that sends a mail to the customer every time an agent answers to the ticket via an article. The trigger sends a mail to the ticket customer and includes the body of the article.
  • When the customer answers from outlook it is correctly received in the ticket.
  • However after a while Outlook throws an error when answering to this automated mail:
550 maximum allowed line length is 998 octets, got 1012

meaning customers are unable to answer the mail.

  • After googling I found out that Outlook has a problem with long headers, so I tried to find why zammads mail headers get too long.

The answer: every time the system sends a mail, the header includes all the previous messages as references like in the example above. Obviously if the conversation in the ticket is getting too long so does the header which Outlook doesnt like very much.

After another googling session I found out that these references are used in mail systems to group mails in conversations when people reply to each other.

I am not sure why zammad uses this method.

p.s.: answering with thunderbird atleast is working with long headers. Unfortunatelly our customers are mainly outlook users and this could trigger a big problem for us.

So my questions:

  1. Is there any better way maybe to send mails to customers AUTOMATICALLY when answering to tickets?
  2. Do you have any other idea how to solve the issue? (Maybe trying to turn off references in mail headers in rails or so?)
  3. Is this maybe a “bug” or something that can be solved in the development? (Don’t fill header with references?)

Steps to reproduce the behavior:

  • create trigger with:
  • article visibility is public
  • action is updated
  • sender is not customer
  • E-Mail
  • Visibility is public
  • recipient is sender of last article and/or customer
  • body include article.body (i guess this isn’t necesarry)
  • now create ticket → set customer → answer to ticket via article → mail should be sent → answer from customers view in outlook mail client-> repeat (article->customer->answer) until headers are too long (about 13 mails in total for me)

Anyone got an idea or knows how to better implement emailing on updates in a ticket? Devs if this is a bug please tell me to move to github with it. Thank you!

I’m not a Dev but adding the reference IDs in the e-mail header is normal behaviour, Outlook does this too. I have never encountered this bug because I have never seen such long conversations. Cut down on the number of e-mails would be my approach. There is a reason why a note and an e-mail are separate things in Zammad.

Thanks for your answer. I know it is normal and Outlook is just not good.

For my understanding. Do you know if sending a mail always requires you to enter the recipient or does the ticket customer always get the mail? Because for me it makes no sense to have a ticket customer when you can’t just simply start typing your reply without having to enter the recipient mailaddress every time.

Have you never used the “Reply” button under any customer note? Of course it adds the e-mail address of the person you are replying to automatically and as a bonus you can use an automatic e-mail signature.
The normal procedure is: you want to write the customer something you hit reply, you just want to add a note you write it in the note field and the customer does not receive an e-mail but can see it in the web ui, you want an internal note you mark it as internal.

Thanks for trying @awedor but:

Just tested it out in a long convo the “reply to” throws the same error in Outlook. So doesn’t matter how you send the mails, if the convo is to long Outlook can’t handle it. Maybe a dev can tell us if the references in the header are mandatory? I know what they are used for in mail software and I am aware that Zammad somehow is kind of a mail programm, but is there maybe a way to make the handling Outlook friendly?

@eeuak Not a DEV, but that seems like an internal issue to your config and how you are using it. In Outlook, references in the header is what ties together emails for a conversation view. I haven’t looked through the coding to see if that is one of the ways Zammad ties a ticket together. If your threads are getting that long, most likely case I’ve seen (from managing/demoing/creating several helpdesks) is that you are using the same ticket for multiple issues, instead of one specific issue. In this system (thankfully) you can link tickets together if they are related, or split them if it contains multiple issues. That way you can properly prioritize and fix issues and mark that specific issue completed.


It is obviously how Zammad ties the messages together. It is definitelly not a config problem since I am just using the internal Mail function. The problem is with outlook, altough there must be a better way to tie messages together since other ticket systems like Jira had no problem with long tickets.

With all due respect but a ticketsystem should have no limitation for the amount of messages regardless of what the ticket is used for.

I know for sure that the problem is with Outlook, but again I would love for a dev to tell me if it would be possible for them to code a message handling that works with outlook?

@eeuak It isn’t a ticket system limitation. Its a microsoft one, that has existed for at least 7 years, that they refuse to fix. If you use an o365 0auth or a microsoft mail server it isnt a problem though. I do think itd be really cool if the devs had a workaround though.

1 Like

For everyone running into this problem:

It seems to only happen with Linux mailservers (exim4) of course Exchange works.

Obviously it was an Outlook only problem nothing to do with Zammad. Anyway if you have this problem with exim this is what I did:

Change config in:



message_size_limit = ${if > {$max_received_linelength}{998} {1}{0}}


message_size_limit = ${if > {$max_received_linelength}{1024} {1}{0}}

basically set the octett limit to 1024, this way Outlook is able to send mails (back to zammad).

Thanks for everyone who tried and I hope this helps someone out!

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