send Message-ID header unconditionally

[slingamn]

Gmail is rejecting messages without Message-ID unconditionally:

:Could not dispatch registration e-mail: 550 5.7.1 [redacted] Messages missing a valid Message-ID header are 5.7.1 not accepted. For more information, go to 5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant and review 5.7.1 RFC 5322 specifications. y7-[redacted] - gsmtp

We send Message-ID iff DKIM is enabled. We should send it in every case.

[slingamn]

Could not dispatch registration e-mail: 550 5.7.1 [redacted] Gmail has detected that this message does not 5.7.1 meet IPv6 sending guidelines regarding PTR records and authentication 5.7.1 . For more information, go to 5.7.1 https://support.google.com/mail/?p=IPv6AuthError [redacted] - gsmtp

Could not dispatch registration e-mail: 550 5.7.26 This mail has been blocked because the sender is unauthenticated. 5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM. 5.7.26 5.7.26 Authentication results: 5.7.26 DKIM = did not pass 5.7.26 SPF [my.network] with ip: [redacted] = did not pass 5.7.26 5.7.26 For instructions on setting up authenticati

It looks like we may need an option to force IPv4/IPv6 for sending (I don't think my provider will give me an IPv6 PTR record).