function protonmail(domain, verification, dkim)
    -- Configure mail records for protonmail

    -- Verification
    txt(domain, "protonmail-verification=" .. verification)

    -- MX records
    mx(domain, "mail.protonmail.ch", 10)
    mx(domain, "mailsec.protonmail.ch", 20)

    -- SPF
    txt(domain, "v=spf1 include:_spf.protonmail.ch mx ~all")

    -- DKIM
    -- TODO: use concat()?
    cname("protonmail._domainkey", "protonmail.domainkey." .. dkim .. ".domains.proton.ch.")
    cname("protonmail2._domainkey", "protonmail2.domainkey." .. dkim .. ".domains.proton.ch.")
    cname("protonmail3._domainkey", "protonmail3.domainkey." .. dkim .. ".domains.proton.ch.")

    -- DMARC
    txt("_dmarc", "v=DMARC1; p=quarantine")
end

function fastmail(domain)
    -- Configure mail records for fastmail
    mx(domain, "in1-smtp.messagingengine.com", 10)
    mx(domain, "in2-smtp.messagingengine.com", 20)
    cname("fm1._domainkey", "fm1." .. domain .. ".dkim.fmhosted.com")
    cname("fm2._domainkey", "fm2." .. domain .. ".dkim.fmhosted.com")
    cname("fm3._domainkey", "fm3." .. domain .. ".dkim.fmhosted.com")
    txt(domain, "v=spf1 include:spf.messagingengine.com ?all")
end

function vanityns(ns1, ns2)
    -- Configure vanity DNS nameservers

    aaaa(concat(ns1, "ns"), "2001:67c:25a0::1")
    a(concat(ns1, "ns"), "185.142.218.1")
    aaaa(concat(ns2, "ns"), "2001:67c:25a0::2")
    a(concat(ns2, "ns"), "185.142.218.2")
end