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A comment on Musl 1.2.4 adds TCP DNS fallback. Parent comment

Re:Musl 1.2.4 adds TCP DNS fallback by vidarh on Sunday July 30, 2023 @04:17PM (#36935493)
It can't use gethostbyname() for looking up MX records, but plenty of mail related software have used it to look up A records.

However musl also includes res_send() etc., which can be used for MX records, and e.g. Qmail did use it back then. Here's the commit adding TCP support to those functions in Musl.

http://git.musl-libc.org/cgit/musl/commit/src/network/res_ms...

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Re:Musl 1.2.4 adds TCP DNS fallback by geocar on Sunday July 30, 2023 @06:09PM (#36936515)
I wasn't aware musl implemented libres. I don't have a problem with libres doing TCP.

Qmail's issue was a hardcoded buffer size so this patch to musl wouldn't have helped.

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Re:Musl 1.2.4 adds TCP DNS fallback by vidarh on Sunday July 30, 2023 @11:48PM (#36938619)
The point wasn't that this would have helped Qmail - Musl didn't exist back then for that matter -, but that running into the 512 byte limit and needing TCP fallback was already a thing. Bumping a buffer size is far less effort than having to replace the resolver.
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