[_el1s7]

> For viva.com's engineering team, in case this reaches you: add a Message-ID header to your outgoing transactional emails.

Don't know what they're using for sending emails, but that's something that should be handled by their email service provider, unless they're hosting their own email servers.

[basilikum]

Interestingly the MX record of via.com points to Google, but their verification emails could come from anywhere of course. The IP address in the log is also a Google IP, although that could also be the receiving IP.

[dathinab]

message-id is (or at least was ~5-10 years ago) only required for automated mails, i.e. if you send a mail which looks mostly the same to a lot of users

so if you (ab-)use protocols for mail clients to send automated mails they might very well not add Message-Id. In general many mail providers have both a way to send a mail where "they do some clever parts" (like adding Message-Id) and interfaces where they mostly just send what you give them. It's possible that they migrated from one solution which did automatically add Message-Id to one using interfaces where it doesn't happen without realizing that there is a mismatch in this solutions do implicitly add.