根据Exim4 文档我有以下脚本：
#! /bin/bash --
ED="dkim_ed25519_$(date +'%Y%m%d')"
RSA="dkim_rsa_$(date +'%Y%m%d')"
## Generate private key
openssl genpkey -algorithm ed25519 -out "${ED}.private"
openssl genrsa -out "${RSA}.private" 2048
## Use private key to generate the public DNS TXT record:
## 20200701._domainkey.example.com IN TXT "k=[ed25519|rsa]; p=[pub_key_content]"
openssl pkey -in "${ED}.private" -pubout -outform DER | tail -c +13 | base64 > "${ED}.public"
openssl rsa -in "${RSA}.private" -pubout -outform PEM | sed '/^-----/d' | tr -d '\n' > "${RSA}.public"
这会生成一对私钥+公钥。公共的有：
dkim_ed25519_20200701.public：
ICkF+6tTRKc8voK15Th4eTXMX3inp5jZwZSu4CH2FIc=
dkim_rsa_20200701.public： …