Temporary failure when sending emails to this mailing list

Hello,

I believe I have discussed this before, but when I email any openbsd
mailing list (or email address) I get the "451 Temporary failure, please
try again later."

My email server passes SPF DKIM and DMARC, has reverse DNS and the IP
address and domain is not listed on any blocklists, it is also
statically allocated, as dynamic addresses are automatically spammed (or
rejected) due to the nature of them changing.

Although my emails eventually go through after about 20-40 minutes of
waiting, it is still incredibly annoying about the length of time I have
to wait for them to be delivered. I have heard this error is due to
spamd where it temporary throttles your email to prevent spam and for
"security purposes", but people who use gmail and outlook do not seem
the have the same issues, so is it simply that my mail server is self
hosted, and therefore not trusted?

I would like to point out I have yet to migrate my mail server from IPv4
to IPv6, but I doubt this is the problem. (I migrated almost everything
else and then got lazy when it comes to mail server, as mail server
configuration is painful).

Any advice would be helpful so I can better interact with the OpenBSD
community (and request more help :P).

Thank you,
--
Polarian
GPG signature: 0770E5312238C760
Website: https://polarian.dev
JID/XMPP: polarian@polarian.dev