dkim-filter fails to work if it cannot open a TCP connection to nameserver port DNS

[Emilio Lucena]

I noticed that when running ubuntu 8.04 Server edition, dkim-filter will work properly if it can not open a TCP connection to the nameserver port DNS. So if, for some reason, your namserver only responds to DNS UDP, you will get an

can't configure DKIM library; continuing

error message. And after that, you will always get an error like:

can't read SMFIC_EOH reply packet header

Maybe dkim-filter should not try to open TCP connection to the nameserver. Instead it should make its queries via UDP.

[Emilio Lucena (ubuntu-vipnetware)]

Actually, I meant to say that the dkim-filter will not work properly if ....

[Simon Déziel (sdeziel)]

I can reproduce this issue too but I doubt that falling back on DNS lookups on UDP only is a good solution. According to this reference http://www.ietf.org/proceedings/42/I-D/draft-ietf-dnsind-udp-size-02.txt the maximum size of a DNS packet in UDP is 512 :
    The Domain Name System defaults to using UDP for queries and replies
    with a DNS payload limit of 512 bytes. Larger replies cause an
    initial truncation indication leading to a subsequent handling via
    TCP with substantially higher overhead.

A lot of DKIM TXT record would not fit in such small packets.

[Scott Kitterman (kitterman)]

Given the size of dkim dns records, trying to do dkim without access to dns over tcp is not likely to end well.