f secure Email message is found suspicious. "Too long header field"

gvaccarello Posts: 21 Explorer

Hello everybody,


Some mails are dropped because the header field is too long. Could you tell me what mean "the header field" and why this is blocked ?


Thanks in advance,






  • Dmitriy
    Dmitriy Posts: 212 F-Secure Employee

    If you can find the blocked email message in the quarantine, open the raw message and check which header and how long it is. If you see a header that exeeds 1024 characters, then it is too long according to RFC. Note that too long header field may indicate that the message is sent a badly designed software (like spammers use) or malicious.

  • gvaccarello
    gvaccarello Posts: 21 Explorer

    thank you for your helpful replies

  • MikaK
    MikaK Posts: 22 F-Secure Product Expert



    We have to have a sample of the email to make further investigation with the issue. Go to FSAV4MSE quarantine and download the email (= header field is too long) as an *.eml format and then send it to our support as a support request.


    Thank you in advance,


  • mahaz
    mahaz Posts: 12

    I guess header field length can be changed in config file. I remember there must be a code like this:


    so changing these limits would impact the header 

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