Unable to send notification emails to a gmail recepient due to missing message-id

[Illuvatar]

I am unable to send notifications to an gmail address using an other provider (hosted at a cpanel-based provider).

The from address is at that provider and receives the bounce:

 

    host gmail-smtp-in.l.google.com [173.194.76.26]
    SMTP error from remote mail server after end of data:
    550-5.7.1 [xxx.xxx.xxx.xxx] Messages missing a valid messageId header are not
    550 5.7.1 accepted. e5-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.xxx - gsmtp

 

I see it both in 6.11.5 and 6.9.2

 

It started a few months ago, so I'm guessing that google started requiring another email header (message-id)

 

As far as I understand/remember SMTP it should be whatever mail-client unraid uses to generate the notification email that is supposed to generate and add the message-id.